Category: Developmental Malformations

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Intraoperative Ultrasound in Chiari 1 Decompression: Clarity or Confusion?

Neurosurgery 99:19–29, 2026

This systematic review evaluates intraoperative ultrasound (iUS) use in guiding the extent of posterior fossa decompression (PFD versus PFD+) for Chiari malformation type 1, analyzing nine studies (844 patients) for iUS criteria, conversion rates, and positive predictive values. It finds substantial heterogeneity in acquisition, qualitative versus quantitative criteria, and outcome reporting, limiting iUS’s reliability for intraoperative decision making.

The authors propose a standardized reporting framework emphasizing defined CSF space measurements, dynamic metrics (e.g., CSF flow velocity, tonsillar excursion), triplicate measurements with dual raters, and ≥12-month validated outcomes to enable reproducible research and clearer assessment of iUS utility.

Clinical dilemma Bone-only posterior fossa decompression (PFD) is less invasive, while dural opening/expansion (PFD+) may be more effective but has higher complication risk; intraoperative ultrasound (iUS) is used to help decide whether PFD alone is sufficient, but its role/criteria are not defined.

Evidence base 9 studies (1 prospective, 8 retrospective) totaling 844 patients (pediatric and adult) were included; risk of bias was low in 1 study, moderate in 3, and high in 5.

How iUS was applied iUS was used after bony decompression and before dural opening; none of the studies used iUS after opening the dura.

Decision criteria heterogeneity 8 studies used qualitative criteria (e.g., “enough space,” tonsillar pulsation, piston-like motion, bidirectional flow), and 1 study used a quantitative CSF flow-velocity threshold.

Conversion surgery outcomes “Conversion” (later revision from PFD to PFD+ due to persistent/worsening symptoms) occurred in 35/844 patients (5% overall), with study-level conversion rates from 0% to 16%.

Predictive value variability Positive predictive value (PPV) for iUS-guided PFD success ranged from 0.857 to 1.000 across studies, varying with criteria and study design.

Main conclusion Current evidence does not support iUS as a robust intraoperative test for deciding extent of decompression because of heterogeneous application and lack of standardized assessment criteria; sensitivity/specificity cannot be determined with available data structure.

Proposed path forward A standardized reporting framework is proposed, emphasizing defined acquisition parameters, quantitative/operationalized criteria, validated outcome measures, and ≥12-month follow-up to enable comparability and future pooled analyses.

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Morphometric assessment of the posterior cranial fossa and its contents in patients with chiari malformation type I and type 0

Acta Neurochirurgica (2026) 168:117

This study presents a retrospective, landmark-based morphometric analysis of the clivus, tentorium, and posterior cranial fossa on midsagittal MRI in 326 subjects, comparing Chiari malformation Type I (CM-I), Chiari Type 0 (CM-0), and matched controls. Key measured parameters include clivus length and angle, tentorial angle, foramen magnum diameter, and area-based ratios relating cerebellum, posterior fossa, and intracranial cavity.

Findings indicate that CM-I patients exhibit clival shortening, reduced posterior cranial fossa area, altered tentorial orientation, and increased cerebellar occupancy relative to posterior fossa and brain, whereas CM-0 patients show morphometry comparable to controls. The authors conclude CM-I has distinct morphoanatomical remodeling, while CM-0 may represent a functional clinical entity without consistent structural substrate.

Definitions: CM-I is defined by ≥5 mm cerebellar tonsillar descent below the foramen magnum on MRI, while CM-0 is defined by <3 mm descent despite Chiari-like symptoms.

Design: Retrospective mid-sagittal MRI morphometry of 326 adults (CM-I n=111, CM-0 n=27, controls n=188) using multiple cranial base, posterior fossa, cerebellar, and intracranial measurements plus area-based ratios.

Key CM-I anatomy: Compared with CM-0 and controls, CM-I showed shorter clivus length, smaller posterior cranial fossa area, and larger cerebellar area; foramen magnum diameter and total brain area were similar across groups.

Crowding ratios: CM-I had higher cerebellum/posterior fossa and cerebellum/brain area ratios, indicating increased relative cerebellar occupancy despite preserved global cranial proportions.

CM-0 vs controls: CM-0 morphometric measurements were largely comparable to healthy controls, with no consistent structural differences in the main posterior fossa metrics highlighted.

Interpretation: CM-I aligns with a pattern of cranial base remodeling and posterior fossa insufficiency, whereas CM-0 may be better viewed as a functionally defined condition rather than one with a consistent structural substrate.

Reliability/statistics: Analyses used nonparametric tests (Kruskal–Wallis with Bonferroni-corrected Mann–Whitney post hoc), and interobserver measurement reliability was good–excellent (ICC 0.82–0.94).

Limitations: Morphometry was 2D mid-sagittal (not full 3D volumetry) and CSF flow dynamics (e.g., phase-contrast MRI) were not uniformly available, limiting functional assessment—especially relevant to CM-0.

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Quality-of-Life Outcomes in Adults and Children With Chiari 1 Malformation and in Those Managed Without Surgery

Neurosurgery 98:1113–1128, 2026

This multicenter prospective study evaluates health-related quality of life (HRQoL) in adults and children with Chiari 1 malformation (CM1) who were managed without surgery, comparing baseline and 12-month patient-reported outcomes. Using SF-36 for adults and PedsQL for children, the UK Chiari 1 Study found baseline HRQoL was lower than normative data but showed overall stability at 12 months for nonsurgical patients.

The study reports symptom prevalence, imaging characteristics, and management decisions across 192 participants, identifying limb and back pain, poor balance, syringomyelia, and psychiatric comorbidity as factors associated with worse HRQoL. Results support cautious nonoperative management for many patients and call for larger, longer-term comparative studies between surgical and nonsurgical care.

Study focus: Prospective, multicenter UK observational cohort measuring health-related quality of life in adults (SF-36) and children (PedsQL) with Chiari 1 malformation (CM1) managed without surgery, from first neurosurgical clinic review to 12 months later.

Baseline HRQoL: Quality-of-life scores at baseline were significantly lower than normative control data across every domain in both adults and children.

Cohort size/follow-up: 192 patients had baseline data; 113 nonsurgical patients had 12-month follow-up data (146 female; 148 adults in baseline cohort).

12-month change (overall): No decreases in quality-of-life subscores over 12 months in adults or children managed without surgery.

Adult improvements: In adults managed without surgery, social functioning and bodily pain SF-36 subscores improved at 12 months (social functioning: t = −4.0, P < .001; bodily pain: t = −2.9, P = .03).

Symptoms at presentation: Headache was most prevalent (79.2% overall), including occipital headache (65.1%) and Valsalva-induced headache (54.2); headache and Valsalva headache were more common in adults than children.

Imaging findings: Median maximum cerebellar tonsillar descent was 10 mm (IQR 7–13); syringomyelia was present in 25.2% of those with spine MRI available for review.

Clinical implications/next steps: HRQoL stability over 12 months supports reassurance/counseling for selected mildly symptomatic or borderline cases, while emphasizing need for robust surgical vs nonsurgical comparisons and longer-term study.

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Health-Related Quality-of-Life Outcomes in Surgical Patients With Sacral Tarlov Cysts: A 2-Year Prospective Study

Neurosurgery 98:1156–1165, 2026

This prospective longitudinal study reports clinical and patient-reported health-related quality-of-life outcomes for 417 adults who underwent surgical treatment for symptomatic sacral Tarlov cysts, with standardized assessments at baseline and 3, 6, 12, and 24 months. Using the disease-specific TCQoL alongside SF-36, ODI, and VAS, the study demonstrates statistically significant and clinically meaningful improvements across most domains, low complication rates, and no radiographic cyst recurrence at early follow-up.

The authors detail a microsurgical posterior sacral laminectomy technique with cyst decompression, dural sleeve wrapping, and laminar reconstruction, and report sustained benefits through 2 years, including increased tolerated sitting time and reduced opioid use. Limitations include attrition and missing data addressed by imputation, and the paper advocates broader adoption of the TCQoL for standardized Tarlov cyst research.

Study aim Assess whether surgical treatment for symptomatic sacral Tarlov cysts improves validated general and disease-specific health-related quality of life (HRQoL) through 2 years post-op, and whether outcomes change from year 1 to year 2.

Design & cohort Retrospective analysis of prospectively collected longitudinal outcomes for adults undergoing first-time surgery for ≥1 sacral Tarlov cyst (2008–2023), performed by a single neurosurgeon; 417 patients (mean age 52.5, 91.1% female).

Outcome measures Primary outcome was the TCQoL (11-item disease-specific scale); secondary measures included VAS pain (rest/activity), ODI, and SF-36, collected pre-op and at 3, 6, 12, and 24 months.

Surgical technique Posterior sacral laminectomy with microsurgical dissection, cyst drainage to normalize root caliber, wrapping the cystic nerve root with bovine pericardium dural substitute sleeve to limit refilling, and covering the laminar window with a resorbable plate/screws.

2-year improvements (key metrics) Significant improvements from pre-op to 2 years in TCQoL (3.2→2.1), VAS pain at rest (4.5→2.3) and activity (5.7→3.1), and ODI (45.5→31.6) (all P<.001).

SF-36 domains Improvement occurred in 7/8 SF-36 scales (Physical Functioning, Physical Limitations, Bodily Pain, Vitality, Social Functioning, Emotional Limitations, Mental Health), while General Health was not statistically significant in the imputed analysis.

Year 1 to year 2 change Most subscales did not change significantly from 1 to 2 years; significant further gains were seen in physical functioning and social functioning (P=.040 and P=.016, respectively).

Sitting tolerance Median tolerated sitting time increased from 15 minutes pre-op to 45 minutes at 2 years post-op.

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Pineal cyst surgery beyond morphology: a critical evaluation of a consecutive surgical series

Acta Neurochirurgica (2026) 168:85

This study evaluates surgical management of symptomatic pineal cysts in a consecutive single-center cohort, comparing microsurgical, endoscopic, and stereotactic techniques. Radiological measures — notably aqueduct diameter and predominant cyst expansion — were analyzed alongside clinical outcomes using the Chicago Chiari Outcome Scale, showing durable benefit when surgery is guided by clinicoradiological criteria.

Findings indicate aqueduct narrowing and anterior expansion better predict positive postoperative outcomes than cyst size alone. Each surgical approach demonstrated specific indications: microsurgery for suspicious lesions, endoscopy for hydrocephalus/anterior compression, and stereotactic drainage for deep or high-risk cases, with overall high rates of sustained improvement.

Clinical problem: Surgical management of pineal cysts is especially controversial in non-hydrocephalic symptomatic patients because clinical–radiological correlations are inconsistent and many studies rely mainly on size/morphology for decisions.

Study design: Retrospective single-center cohort of 46 symptomatic pineal cyst patients (2008–2024), comparing surgical (n=18) vs non-surgical (n=28) groups and analyzing radiological markers (e.g., cyst dimensions, aqueduct diameter, predominant expansion) alongside outcomes measured by CCOS over time.

Key differentiators for surgery: Compared with non-surgical patients, surgical patients had larger cysts, narrower aqueducts (0.9 vs 1.6 mm, p<0.001), and much more frequent predominant anterior expansion (67% vs 7%, p<0.001).

Overall outcomes: After surgery, 94% achieved good/excellent CCOS (≥12) at 12 months, and 93% maintained good/excellent outcomes at long-term follow-up (mean 62 months).

Predictors: Aqueduct diameter was more closely associated with outcome than pineal cyst size; neither cyst volume nor hydrocephalus consistently predicted postoperative outcome.

Technique comparison: Microsurgical resection (n=12) had favorable long-term outcomes (mean CCOS 14.9) but the highest complication rate (3 patients) and the highest recurrence of headache despite total excision.

Endoscopic approach: Endoscopic fenestration + ventriculostomy (n=3) produced the best long-term outcomes (mean CCOS 15.7) with no recurrences reported.

Stereotactic option: Stereotactic drainage + Rickham reservoir (n=3) achieved stable decompression but lower long-term CCOS (mean 13.0) than other approaches.

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Suprasellar Versus Third Ventricular Cysts: Anatomic and Surgical Considerations

Operative Neurosurgery 30:468–471, 2026

This surgical case instruction contrasts suprasellar arachnoid cysts (SACs) and third ventricular cysts (3VCs), emphasizing their distinct imaging features, clinical presentations, and risks of obstructive hydrocephalus. It summarizes patient examples, MRI findings, and outcomes after endoscopic cyst fenestration, demonstrating restoration of cerebrospinal fluid flow and symptom resolution.

The article details stepwise endoscopic techniques—cyst plane development, wall reduction, excision, and membrane management—highlighting anatomical cues that guide whether endoscopic third ventriculostomy is necessary. Practical tips on preserving hypothalamic structures, restoring aqueduct patency, and minimizing reaccumulation are provided for neurosurgical practice.

Prevalence Intracranial arachnoid cysts occur in ~2.6% of children and ~1.4% of adults; suprasellar arachnoid cysts (SACs) comprise ~9%–21% of pediatric arachnoid cysts and can be confused with rarer third ventricular cysts (3VCs).

Presentation SACs and 3VCs often enlarge and cause obstructive hydrocephalus with symptoms of increased intracranial pressure, prompting urgent treatment to restore CSF circulation.

Imaging differences (SAC) SACs elevate the third ventricular floor, displace mammillary bodies superiorly/posteriorly, and elongate/stretch the midbrain and aqueduct, with aqueduct occlusion from distortion and the posterior cyst wall.

Imaging differences (3VC) 3VCs displace the third ventricular floor and mammillary bodies inferiorly with midbrain compaction; the aqueduct is obstructed by midbrain distortion and the inferoposterior cyst wall.

Treatment rationale A shunt without cyst fenestration can lead to asymmetric hydrocephalus and/or continued cyst enlargement due to cyst-related occlusion of the foramina of Monro; neuroendoscopy enables cyst fenestration with low morbidity risk at experienced centers.

Endoscopic steps A stepwise intraventricular endoscopic approach includes: developing the cyst/ventricle plane; reducing cyst wall size (coagulation); excising roof/lateral/medial walls (with caution laterally in SACs due to hypothalamic fusion); removing/reducing floating membranes (especially posteriorly) to open access to the aqueduct.

Inferior wall strategy In SACs, inferior membrane fenestration may be unnecessary because the prepontine cistern is already exposed/communicates with the third ventricle; in 3VCs, the inferior aspect is the third ventricular floor, and endoscopic third ventriculostomy (ETV) is an option.

ETV decision point If posterior membrane resection fully restores aqueduct patency, ETV may not be necessary; reducing expansile membranes is pursued to lower risk of reaccumulation from scarring.

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Optimal imaging follow-up strategies for conservatively managed cerebral cavernous malformations: a cost-effectiveness analysis

J Neurosurg 143:1555–1566, 2025

This study evaluates cost-effectiveness of MRI surveillance intervals for conservatively managed cerebral cavernous malformations (CCMs) using a Markov model and Monte Carlo simulations. It compares 0.5-, 1-, 2-, and 3-year follow-up strategies for brainstem versus nonbrainstem CCMs, calculating lifetime costs, QALYs, and net monetary benefit from a US societal perspective.

Results indicate annual MRI is most cost-effective for brainstem CCMs, while a 3-year MRI interval is preferred for nonbrainstem CCMs, with findings robust to sensitivity analyses that varied hemorrhage rates, mortality, and MRI costs. The authors emphasize individualized follow-up based on symptoms, Zabramski grade, family history, and lesion multiplicity, and note model limitations and US-centric cost data.

Optimal MRI Follow-up for Brainstem CCM: Annual MRI follow-up (every 1 year) is the most cost-effective strategy for conservatively managed, unruptured brainstem cerebral cavernous malformations (CCM), balancing cost and quality-adjusted life years (QALYs).

Optimal MRI Follow-up for Nonbrainstem CCM: MRI follow-up every 3 years is the most cost-effective approach for nonbrainstem CCM, with less frequent imaging justified by lower rupture and rehemorrhage rates.

Markov Model and Monte Carlo Simulation: A decision-analytic Markov model with Monte Carlo simulations was used to compare different MRI follow-up intervals (0.5, 1, 2, and 3 years) for both brainstem and nonbrainstem CCM, incorporating costs, effectiveness (QALYs), and net monetary benefit (NMB).

Key Drivers of Cost-effectiveness: The cost-effectiveness of follow-up strategies is highly sensitive to annual rates of CCM rupture, mortality after rupture, and the cost of MRI; higher hemorrhage or mortality rates favor more frequent imaging.

Individualization of Follow-up: Follow-up intervals should be tailored based on lesion location, symptoms, prior hemorrhage, Zabramski grade, family history, and multiplicity, as higher-risk patients may benefit from closer surveillance.

Brainstem Lesion Risks: Brainstem CCMs have higher annual rupture (2.8%) and rehemorrhage rates (32.3%) compared to nonbrainstem lesions, resulting in greater disability and loss of quality of life, justifying more vigilant follow-up.

MRI Cost Thresholds: As the annual MRI cost increases above $6,581 for brainstem CCM and $8,995 for nonbrainstem CCM, less frequent MRI follow-up (every 2 years) becomes more cost-effective than the previously optimal intervals.

Limitations: The model does not distinguish between cerebellar and supratentorial nonbrainstem lesions, does not account for comorbidities or detailed imaging findings (e.g., Zabramski grade), and uses US-based cost data, which may limit generalizability to other healthcare settings.

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Cognitive-Affective Improvement on Cerebellar Neuropsychiatric Rating Scale Scores in Adults and Children After Decompression of Chiari Malformation Type I

Neurosurgery 97:1450–1458, 2025

This clinical study assesses the Cerebellar Neuropsychiatric Rating Scale (CNRS) applied to adults and children with symptomatic Chiari Malformation Type I undergoing posterior fossa decompression. Preoperative and 8–24 month postoperative CNRS scores in 87 patients (56 follow-up) showed significant reductions in total, attentional, emotional, and autism-spectrum symptoms, with feasible administration under 15 minutes.

Correlations linked higher preoperative CNRS scores to worse neuropsychological test performance and poorer Chicago Chiari Outcome Scale subscores for attention and autism domains. Exploratory factor analysis supported five interpretable CNRS factors, suggesting CNRS as a practical perioperative patient-reported tool to capture cognitive-affective outcome domains complementary to standard functional metrics.

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Surgical outcomes for spinal arachnoid cysts and webs: a case series

Acta Neurochirurgica (2025) 167:248

This retrospective case series found that surgical treatment for spinal arachnoid cysts (SAC) and webs (SAW) resulted in favorable outcomes (mMC I-II) in 90% and 83% of patients, respectively, with low complication and recurrence rates. Surgery should be considered for symptomatic patients.

• Spinal arachnoid cysts (SAC) and spinal arachnoid webs (SAW) are rare intradural pathologies causing pain and myelopathic symptoms.

• MRI is the main diagnostic tool, but distinguishing between SAC and SAW can be difficult; both may show the “scalpel sign”.

• This retrospective study reviewed 35 patients (29 SAC, 6 SAW) treated surgically from 2011–2023.

• Most patients presented with pain, gait disturbance, sensory, or motor deficits; preoperative neurological status was often not severe.

• Surgical treatment (fenestration or resection) led to favorable outcomes (mMC I-II) in 90% of SAC and 83% of SAW patients.

• Complications occurred in 14.7% of SAC cases but resolved without lasting deficits; no complications in SAW group.

• Recurrence was rare (2.7% in SAC, none in SAW) during short-term follow-up.

• Surgery is recommended for symptomatic patients, with generally favorable short-term results, but larger and longer-term studies are needed.

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Symptomatic Progression, Recurrence, and Long-Term Follow-Up of Patients With Intracranial Epidermoid Cysts

Neurosurgery 97:351–360, 2025

This retrospective study of 146 patients with intracranial epidermoid cysts found that recurrence is common after subtotal resection, but most patients experience significant symptomatic improvement post-surgery. Intraoperative lumbar drain placement increased 30-day readmission risk, and malignant transformation was exceedingly rare. Mortality was not observed.

• Intracranial epidermoid cysts are rare, slow-growing tumors, often presenting with cranial nerve dysfunction, headaches, vertigo, and seizures.

• Surgical resection is standard, but complete removal is often limited by adherence to critical neurovascular structures, leading to frequent residual tumor.

• Recurrence is common, especially after subtotal resection; radiologic evidence of residual tumor predicts shorter recurrence-free survival.

• Most patients show significant symptomatic improvement after surgery, with over half asymptomatic at latest follow-up, even if reoperations are needed.

• 30-day readmission rate is over 10%, mainly due to CSF leaks and aseptic meningitis; intraoperative lumbar drain placement increases readmission risk.

• Malignant transformation to squamous cell carcinoma is exceedingly rare (less than 0.05%).

• No deaths related to tumor or treatment were observed in this large cohort.

• Maximal safe resection is recommended to minimize recurrence, but complete capsule removal is often not feasible.

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Comparison of suboccipital craniectomy versus suboccipital cranioplasty in foramen magnum decompression for adult Chiari malformation

J Neurosurg Spine 43:237–245, 2025

This retrospective study compared suboccipital craniectomy and cranioplasty for foramen magnum decompression in adult Chiari malformation. Both techniques improved symptoms and syrinx size, but cranioplasty incurred higher costs without significant clinical or radiological advantages. Cost considerations should be discussed during shared decision-making.

• Suboccipital craniectomy and suboccipital cranioplasty are two surgical techniques for foramen magnum decompression (FMD) in adult Chiari malformation.

• Both procedures significantly improve preoperative symptoms and reduce syrinx size, with no significant difference in clinical outcomes.

• Suboccipital craniectomy results in a greater increase in subarachnoid space compared to cranioplasty.

• No significant differences were found in surgical time, estimated blood loss, or cervical alignment between the two groups.

• Suboccipital cranioplasty incurs higher daily medical costs due to the use of plates and screws for bony reconstruction.

• Both techniques have similar rates of complications and secondary surgeries.

• The additional costs of cranioplasty should be discussed with patients during shared decision-making.

• Study limitations include retrospective design, small sample size, surgeon preference, and shorter follow-up for cranioplasty.

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Measurement of CSF flow and brain motion in Chiari malformation type I subjects undergoing posterior fossa decompression surgery

J Neurosurg 143:13–23, 2025

Advanced MRI techniques show that in Chiari malformation type I, presurgical CSF flow and brain motion measurements better predict improvements after posterior fossa decompression surgery than traditional tonsillar descent metrics, potentially enabling more accurate identification of patients likely to benefit from surgery.

• Chiari malformation type I (CM-I) is defined by ≥5 mm cerebellar tonsil herniation through the foramen magnum, but tonsillar descent does not correlate well with symptom severity or surgical outcome.

• Posterior fossa decompression (PFD) surgery improves symptoms in ~75% of symptomatic CM-I patients, but carries risks, making optimal patient selection important.

• This study used advanced MRI (phase-contrast for CSF flow and DENSE for brain motion) to evaluate 108 CM-I patients, 61 of whom had PFD surgery.

• After PFD, CSF stroke volume increased by 28.9%, brainstem motion decreased by 17.3%, and cerebellar motion decreased by 45.2%.

• Improvements in CSF flow and brain motion after surgery were better predicted by presurgical CSF flow and brain motion, not by the amount of tonsillar descent.

• Presurgical dynamic measures (CSF flow, brain motion) are more informative for predicting surgical benefit than conventional anatomical metrics.

• These quantitative imaging assessments may help identify which patients will benefit most from surgery, improving patient care.

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Predecompression and postdecompression cognitive and affective changes in Chiari malformation type I

J Neurosurg 143:4–12, 2025

This prospective study found that patients with Chiari malformation type I commonly experience cognitive and psychiatric impairments, particularly in executive function and visuospatial memory. Following posterior fossa decompression surgery, 89% showed significant improvement in cognitive and/or psychiatric symptoms, highlighting the cerebellum’s role in these functions.

• Chiari malformation type I (CM-I) patients often have unrecognized cognitive and psychiatric symptoms, including deficits in executive function, visuospatial memory, and increased depression, anxiety, and related symptoms.

• This prospective study assessed 54 CM-I patients with cognitive or psychiatric complaints before and after posterior fossa decompression (PFD) surgery.

• Preoperatively, patients performed worse than normative samples in executive function and visuospatial memory, and reported more psychiatric symptoms across all measured domains.

• Six months after surgery, 89% of patients showed clinically significant improvements (>1 SD) in cognitive and/or psychiatric domains.

• Improvements were most notable in visuospatial memory and psychiatric symptoms such as depression and anxiety, which normalized to levels seen in the general population.

• Patients with the most severe preoperative deficits experienced the greatest postoperative improvements.

• The findings support a key role for the cerebellum in cognitive and psychiatric dysfunction and suggest that some symptoms in CM-I are potentially treatable with targeted cerebellar intervention.

• Limitations include lack of a control group and focus on symptomatic, self-reporting patients, so results may not generalize to all CM-I cases.

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A Staged Approach for Surgical Management of Basilar Invagination

Operative Neurosurgery 27:424–430, 2024

Patients with basilar invagination (BI) can be treated with several surgical options, ranging from simple posterior decompression to circumferential decompression and fusion. Here, we aimed at examining the indications and outcomes associated with these surgical strategies to devise a staged algorithm for managing BI.

METHODS: We conducted a retrospective cohort study in 2 neurosurgical centers and included patients with a BI, as defined by a position of the dens tip at least 5 mm above the Chamberlain line. Other craniovertebral junction anomalies, such as atlas assimilation, platybasia, and Chiari malformations, were documented. C1-C2 stability was assessed with a dynamic computed tomography scan.

RESULTS: We included 30 patients with BI with a mean follow-up of 56 months (min = 12, max = 166). Posterior decompression and fusion (n = 8) was only performed in cases of obvious atlanto-axial instability (eg, increased atlanto-dental interval or hypermobility on flexion/extension), while anterior decompression (transoral or transnasal) was reserved to patients with lower cranial nerves deficits (eg, swallowing dysfunction) and irreducible anterior compression (n = 9). Patients with posterior signs (eg, Valsalva headaches) or myelopathy but without C1-C2 instability nor anterior signs were managed with an isolated foramen magnum decompression, with or without duraplasty (n = 13). Complications were more frequent for combined procedures, including neurological deterioriation (n = 4) and tracheostomy (n = 2), but reinterventions were more likely in patients undergoing posterior decompression alone (n = 3).

CONCLUSION: Patient selection is key to determine the appropriate surgical strategy for BI: In our experience, combined approaches are only needed for patients with irreducible and symptomatic anterior compression, while fusion should be restricted to patient with obvious signs of atlanto-axial instability. Other BI patients can be managed by foramen magnum decompression alone to minimize surgical morbidity.

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Familial Chiari malformation: a systematic review and illustrative cases

J Neurosurg Spine 41:105–114, 2024

Chiari malformations (CMs) are a group of congenital or acquired disorders characterized by hindbrain overcrowding into an underdeveloped posterior cranial fossa. CM is considered largely sporadic—however, there exists growing evidence of transmissible genetic underpinnings. The purpose of this systematic review of all familial studies of CM was to investigate the existence of an inherited component and provide recommendations to manage and monitor at-risk family members.

METHODS This paper includes the following: 1) a unique case report of dizygotic twins who presented at the Toronto Western Hospital Spinal Cord Clinic with symptomatic CM type 1 (CM-1) and syringomyelia; and 2) a systematic review of familial CM. The EMBASE and MEDLINE databases were searched on June 27, 2023, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Only articles in the English language concerning the diagnosis of CM in > 1 human family member presented as a case study, case series, or literature review were included.

RESULTS Among the 29 articles included in the final analysis, a total of 34 families with CM were analyzed. An average of 3 cases of CM were found per family among all generations. Eighty-one cases (88%) reported CM-1, whereas the other 11 (12%) cases reported either CM-0, CM-1.5, or tonsillar ectopia. A syrinx was present in 37 (54%) cases, with 14 (38%) of these patients also reporting a skeletal abnormality, the most common comorbidity. Most family members diagnosed with CM were siblings (18; 35%), followed by monozygotic twins/triplets (12; 23%).

CONCLUSIONS Patients most often presented with headaches, sensory disturbances, or generalized symptoms. Overall, there exists mounting evidence for a hereditary component of CM. It is unlikely to be explained by a classic mendelian inheritance pattern, but is rather a polygenic architecture influenced by variable penetrance, cosegregation, and entirely nongenetic factors. For first-degree relatives of those affected by CM, the authors’ findings may influence clinicians to conduct closer clinical and radiographic monitoring, promote patient education, and consider earlier genetic testing.

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Sacral Tarlov perineurial cysts: a systematic review of treatment options

J Neurosurg Spine 40:375–388, 2024

Tarlov perineurial spinal cysts (TCs) are an underrecognized cause of spinal neuropathic symptoms. TCs form within the sensory nerve root sleeves, where CSF extends distally and can accumulate pathologically. Typically, they develop at the sacral dermatomes where the nerve roots are under the highest hydrostatic pressure and lack enclosing vertebral foramina. In total, 90% of patients are women, and genetic disorders that weaken connective tissues, e.g., Ehlers-Danlos syndrome, convey considerable risk. Most small TCs are asymptomatic and do not require treatment, but even incidental visualizations should be documented in case symptoms develop later. Symptomatic TCs most commonly cause sacropelvic dermatomal neuropathic pain, as well as bladder, bowel, and sexual dysfunction. Large cysts routinely cause muscle atrophy and weakness by compressing the ventral motor roots, and multiple cysts or multiroot compression by one large cyst can cause even greater cauda equina syndromes. Rarely, giant cysts erode the sacrum or extend as intrapelvic masses. Disabling TCs require consideration for surgical intervention.

The authors’ systematic review of treatment analyzed 31 case series of interventional percutaneous procedures and open surgical procedures. The surgical series were smaller and reported somewhat better outcomes with longer term follow-up but slightly higher risks. When data were lacking, authorial expertise and case reports informed details of the specific interventional and surgical techniques, as well as medical, physical, and psychological management.

Cyst-wrapping surgery appeared to offer the best longterm outcomes by permanently reducing cyst size and reconstructing the nerve root sleeves. This curtails ongoing injury to the axons and neuronal death, and may also promote axonal regeneration to improve somatic and autonomic sacral nerve function.

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A novel classification and management scheme for craniocervical junction disorders with ventral neural element compression

J Neurosurg 140:585–594, 2024

Craniocervical junction (CCJ) pathologies with ventral neural element compression are poorly understood, and appropriate management requires accurate understanding, description, and a more uniform nomenclature. The aim of this study was to evaluate patients to identify anatomical clusters and better classify CCJ disorders with ventral compression and guide treatment.

METHODS A retrospective review of adult and pediatric patients with ventral CCJ compression from 2008 to 2022 at a single center was performed. The incidence of anatomical abnormalities and compressive etiologies was assessed. Surgical approach, radiographic data, and outcomes were recorded. Association rules analysis (ARA) was used to assess variable clustering.

RESULTS Among 51 patients, the main causes of compression were either purely bony (retroflexed dens [n = 18]; basilar invagination [BI; n = 13]) or soft tissue (degenerative pannus [n = 16]; inflammatory pannus [n = 2]). The primary cluster in ARA was a retroflexed dens, platybasia, and Chiari malformation (CM), and the secondary cluster was BI, C1–2 subluxation, and reducibility. These, along with degenerative pannus, formed the three major classes. In assessing the optimal treatment strategy, reducibility was evaluated. Of the BI cases, 12 of the 13 patients had anterolisthesis of C1 that was potentially reducible, compared with 2 of the 18 patients with a retroflexed dens (both with concomitant BI), and no pannus cases. The mean C1–2 facet angle was significantly higher in BI at 32.4°, compared with −2.3° in retroflexed dens and 8.1° in degenerative pannus (p < 0.05). Endonasal decompression with posterior fixation was performed in 48 (94.0%) of the 51 patients, whereas posterior reduction/fixation alone was performed in 3 patients (6.0%). Of 16 reducible cases, open posterior reduction alone was successful in 3 (60.0%) of 5 cases, with all successes containing isolated BI. Reduction was not attempted if vertebral anatomy was unfavorable (n = 9) or the C1 lateral mass was absent (n = 5). The mean follow-up was 28 months. Symptoms improved in 88.9% of patients and were stable in the remaining 11.1%. Tracheostomy and percutaneous G-tube placement occurred in 7.8% and 11.8% of patients, respectively. Reoperation for an endonasal CSF leak repair or posterior cervical wound revision both occurred in 3.9% of patients.

CONCLUSIONS In classifying, one cluster caused decreased posterior fossa volume due to an anatomical triad of retroflexed dens, platybasia, and CM. The second cluster caused pannus formation due to degenerative hypertrophy. For both, endonasal decompression with posterior fixation was ideal. The third group contained C1 anterolisthesis characterized by a steep C1–2 facet angle causing reducible BI. Posterior reduction/fixation is the first-line treatment when anatomically feasible or endonasal decompression with in situ posterior fixation when anatomical constraints exist.

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The influence of tumor topography on the surgical outcome of craniopharyngiomas

J Neurosurg 139:1247–1257, 2023

Various topographical classifications for craniopharyngioma have been proposed based on their relationship with optic chiasm and the third ventricular floor. There is a paucity of literature evaluating the surgical outcome based on tumor topography. This study aims to compare the surgical outcomes of retrochiasmatic craniopharyngiomas (RCPs) and nonretrochiasmatic craniopharyngiomas (non-RCPs).

METHODS This retrospective study includes newly diagnosed patients with craniopharyngioma who underwent surgery between January 2000 and December 2015. Clinical features, the extent of resection (EOR), surgical outcomes, tumor recurrence, and progression-free survival (PFS) of craniopharyngiomas were compared with respect to their relationship to the optic chiasm and third ventricular floor.

RESULTS The authors identified RCPs in 104 and non-RCPs in 33 patients. RCPs were significantly larger and more associated with hydrocephalus than were non-RCPs (p < 0.001) at the time of diagnosis. Puget grade 2 hypothalamic involvement was more frequent with RCPs. EOR and PFS following either subtotal resection (p = 0.07) or gross-total resection (p = 0.7) were comparable between RCPs and non-RCPs. There was no significant difference in the postoperative visual outcome. Resection of RCPs resulted in higher postoperative hypopituitarism (64% vs 42%, p = 0.01) and hypothalamic dysfunction (18% vs 3%, p = 0.02). Location of the tumor, either retrochiasmatic (HR 0.5; 95% CI 0.14–2.2; p = 0.4) or nonretrochiasmatic (HR 1.3; 95% CI 0.3–5.5; p = 0.6), did not show association with recurrence. RCPs with extraand intraventricular components (type 3b) had a higher incidence of postoperative hypothalamic morbidities (p = 0.01) and tumor recurrence (36% vs 19%; p = 0.05) during follow-up than the extraventricular (type 3a) RCP. Between prechiasmatic and infrachiasmatic/intrasellar craniopharyngiomas, EOR (p = 0.7), postoperative diabetes insipidus (p = 0.4), endocrinological outcome (p = 0.7), and recurrence (p = 0.1) were comparable. The patients with complex multicompartmental tumors had a lower rate of gross-total resection (25%, p = 0.02) and a higher incidence of tumor recurrence (75%, p = 0.004) than the rest.

CONCLUSIONS The tumor topography can influence the postoperative outcome. RCPs can be associated with a higher incidence of hypopituitarism and hypothalamic morbidities postoperatively. The influence of topography on EOR and tumor recurrence is controversial. However, this study did not find a significant difference in EOR and tumor recurrence between RCPs and non-RCPs. PFS and overall mortality are also comparable.

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Predictors of extent of resection and recurrence following endoscopic endonasal resection of craniopharyngioma

J Neurosurg 139:1235–1246, 2023

Craniopharyngioma is a benign but surgically challenging brain tumor. Controversies exist regarding its ideal treatment strategy, goals of surgery, efficacy of radiation, and the long-term outcomes of these decisions. The authors of this study performed a detailed analysis of factors predictive of the extent of resection and recurrence in large series of craniopharyngiomas removed via an endoscopic endonasal approach (EEA) with long-term follow-up.

METHODS From a prospective database of all EEAs done at Weill Cornell Medical College by the senior author from 2004 to 2022, a consecutive series of histologically proven craniopharyngiomas were identified. Gross-total resection (GTR) was generally the goal of surgery. Radiation was often given if GTR had not been achieved. The stalk was preserved if not infiltrated with tumor but was sacrificed to achieve GTR. Intentional subtotal resection (STR) was performed in select cases to avoid hypothalamic injury.

RESULTS Among the 111 identified cases were 88 adults and 23 children. Newly diagnosed cases comprised 58.6% of the series. GTR was attempted in 77.5% of the patients and among those cases was achieved in 89.5% of treatmentnaive tumors and 72.4% of recurrent tumors. An inability to achieve GTR was predicted by prior surgical treatment (OR 0.13, 95% CI 0.03–0.6, p = 0.009), tumor diameter ≥ 3.5 cm (OR 0.11, 95% CI 0.02–0.53, p = 0.006), and encasement of the optic nerve or a major artery (OR 0.11, 95% CI 0.01–0.8, p = 0.03). GTR with stalk preservation maintained some anterior pituitary function in 64.5% of cases and prevented diabetes insipidus in 25.8%. After a median follow-up of 51 months (IQR 17–80 months), the recurrence rate after GTR was 12.5% compared with 38.5% after non-GTR. The median recurrence-free survival was 5.5 years after STR, 8.3 years after near-total resection (≥ 98%), and not reached after GTR (p = 0.004, log-rank test). GTR was the strongest predictor of recurrence-free survival (OR 0.09, 95% CI 0.02–0.42, p = 0.002), whereas radiation did not show a statistically significant impact (OR 1.17, 95% CI 0.45–3.08). In GTR cases, the recurrence rate was higher if the stalk had been preserved (22.6%) as opposed to a sacrificed stalk (4.9%; OR 5.69, 95% CI 1.09–29.67).

CONCLUSIONS The study data show that GTR should be the goal of surgery in craniopharyngiomas if it can be achieved safely. Although stalk preservation can maintain some endocrine function, the risk of recurrence is higher in such cases. Radiation may not be as effective as previously reported.

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Posterior Fossa Midline Epidermoid Tumors: Role of the Inferior Medullary Velum and a Proposed New Imaging Classification

Neurosurgery 93:112–119, 2023

Posterior fossa midline epidermoid tumors (PFMETs) include the epidermoid tumors of the cisterna magna (CM) and fourth ventricle (FV).

OBJECTIVE: To report tumor epicenter-based classification of PFMETs and its clinical and surgical implications with outcome. METHODS: On retrospective analysis of operated cases of intracranial epidermoid tumors, 19 (N = 19) patients having tumor epicenter within FV, CM, or both were included. Cerebellopontine and prepontine cistern epidermoid were excluded. Tumor location was decided based on preoperative MRI and intraoperative findings. Major complication was defined as new onset or worsening of cranial nerve (CN) deficit, sensory motor impairment, or tracheostomy.

RESULTS: The mean (±SD) age of the patients was 42.0 ± 11.6 years (range 25-61 years), with no sex predilection (male: female: 1:0.9). The most common symptoms were cerebellar dysfunction, headache, vomiting, and diplopia. Common CNs affected were VII, V, lower cranial nerve, and VI. The PFMETs were classified based on tumor epicenter as type 1 (tumor epicenter in CM, n = 4/21.1%), type 2 (FV, n = 5/26.3%), and type 3 (involved CM and FV, n = 10/52.6%). Type 2 tumors had a higher incidence of raised intracranial pressure and only facial nerve palsy as preoperative CN deficit. Type 1 tumors had the least incidence of postoperative major complications. Type 3 tumors were the largest and had a greater incidence of brainstem adhesion and postoperative complications. The tumor size, duration of symptoms, and patient age were higher in patients with brainstem adhesion (5.3 ± 1.0 cm, 21 ± 16 months, 44.1 ± 9.2 years) as against its absence (4.8 ± 1.3 cm, 11.2 ± 7.3 months, 38.2 ± 11.7 years). Inferior medullary velum and tela choroidea have a critical role in tumorogenesis, tumor extension, and brainstem adhesion.

CONCLUSION: PFMETs can be classified into 3 subtypes based on tumor epicenter having clinical and surgical implications. Less aggressive dissection and near total excision in the presence of brainstem adhesion yield favorable outcomes.

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