Feasibility of occipital condyle screw placement in patients with Chiari malformation type I

Acta Neurochirurgica (2021) 163:1569–1575

The occipital condyle (OC) screw is an alternative technique for occipitocervical fixation that is especially suitable for revision surgery in patients with Chiari malformation type I (CMI). This study aimed to investigate the feasibility and safety of this technique in patients with CMI.

Methods The CT data of 73 CMI patients and 73 healthy controls were retrospectively analyzed. The dimensions of OCs, including length, width, height, sagittal angle, and screw length, were measured in the axial, sagittal, and coronal planes using CT images. The OC available height was measured in the reconstructed oblique parasagittal plane of the trajectory.

Results The mean length, width, and height of OCs in CMI patients were 17.79   2.31 mm, 11.20   1.28 mm, and 5.87   1.29 mm, respectively. All OC dimensions were significantly smaller in CMI patients compared with healthy controls. The mean screw length and sagittal angle were 19.13   1.97 mm and 33.94    5.43 , respectively. The mean OC available height was 6.36   1.59 mm. According to criteria based on OC available height and width, 52.1% (76/146) of OCs in CMI patients could safely accommodate a 3.5-mm-diameter screw.

Conclusions The OC screw is feasible in approximately half of OCs in CMI patients. Careful morphometric analyses and personalized surgical plans are necessary for the success of this operation in CMI patients.

Occipitocervical Instability After Far-Lateral Transcondylar Surgery

Neurosurgery 80:140–145, 2017

After a far-lateral transcondylar approach, patients may maintain neutral alignment in the immediate postoperative period, but severe occipitoatlantal subluxation may occur gradually with cranial settling and possible neurological injury. Previous research is based on assumptions regarding the extent of condylar resection and the change in biomechanics that produces instability.

OBJECTIVE: To quantify the extent of bone removal during a far-lateral transcondylar approach, determine the changes in range of motion (ROM) and stiffness that occur after condylar resection, and identify the threshold of condylar resection that predicts alterations in occipitocervical biomechanics.

METHODS: Nine human cadaveric specimens were biomechanically tested before and after far-lateral transcondylar resection extending into the hypoglossal canal (HC). The extent of condylar resection was quantified using volumetric comparison between pre- and postresection computed tomography scans. ROM and stiffness testing were performed in intact and resected states. The extent of resection that produced alterations in occipitocervical biomechanics was assessed with sensitivity analysis.

RESULTS: Bone removal during condylar resection into the HC was 15.4%-63.7% (mean 35.7%). Sensitivity analysis demonstrated that changes in biomechanics may occur when just 29% of the occipital condyle was resected (area under the curve 0.80-1.00).

CONCLUSION: Changes in occipitocervical biomechanics may be observed if one-third of the occipital condyle is resected. During surgery, the HC may not be a reliable landmark to guide the extent of resection. Patients who undergo condylar resections extending into or beyond the HC require close surveillance for occipitocervical instability.

Atlanto-occipital Instability Following Endoscopic Endonasal Approach for Lower Clival Lesions

Atlanto-occipital Instability Following Endoscopic Endonasal Approach for Lower Clival Lesions

Neurosurgery 77:888–897, 2015

The endoscopic endonasal approach (EEA) for craniocervical lesions involving the lower clivus and occipital condyles carries an unclear risk of atlantooccipital (AO) instability requiring arthrodesis.

OBJECTIVE: Elucidate risk factors for AO instability following EEA for clival lesions.

METHODS: We reviewed patients with clival tumors who underwent EEA at our institution between 2002 and 2012. Resection of the lower clivus, foramen magnum, AO joint, and occipital condyles were evaluated on fine-cut postoperative computed tomography.

RESULTS: Two hundred twelve patients (mean age 47.9 years, 57.1% male) underwent transclival EEA for lower clival lesions. In addition to the lower clivus, resection involved the condyle in 14.2% of patients, the foramen magnum in 16.5%, and the AO joint in 1.4%. Quantification of condyle resection revealed complete resection in 3 cases, 75% resection in 8 cases, 50% resection in 6 cases, and 25% resection in 13 cases. Seven of these patients had EEA combined with an open, far-lateral approach. In total, 7 patients required arthrodesis following EEA (3.3%), 4 of them after a combined approach. All patients who underwent arthrodesis had primary bone tumors such as chordoma, chondrosarcoma, or osteosarcoma (P = .022). Degree of condyle resection was a significant factor predisposing to occipitocervical instability (P = .001 and P < .001 for 75% and 100% condyle resection, respectively). Use of a combined approach was significantly associated with arthrodesis (P < .001).

CONCLUSION: EEA resection of the occipital condyles that results in greater than 75% condyle resection or EEA in combination with an open approach significantly increases the risk of AO instability and likely necessitates AO fixation.

Microsurgical Management of Hypoglossal Schwannomas Over 3 Decades: A Modified Grading Scale to Guide Surgical Approach

Neurosurgery 69[ONS Suppl 2]:ons121–ons140, 2011. DOI: 10.1227/NEU.0b013e31822a547b

Schwannomas originating from the hypoglossal nerve are extremely rare. Microsurgical resection with the goal for cure has traditionally been associated with a high risk of postoperative deficits.

OBJECTIVE: To summarize our clinical experience using tailored cranial base approaches for these formidable lesions.

METHODS: The clinical records of 13 patients were retrospectively reviewed. In addition, all reported patients in the literature were reviewed. The extreme lateral infrajugular transcondylar-transtubercular exposure approach was used in all of our patients. Based on our experience and literature analysis, we propose the following modified grading scale to facilitate surgical planning: type A, intradural tumors; type B, dumbbell-shaped tumors; type C, extracranial tumors; and type D, peripheral tumors.

RESULTS: All 13 patients underwent total, near-total, or subtotal tumor resection. Eight patients were men, 5 were women (mean age, 41.7 years). Sural nerve graft reconstruction for the hypoglossal nerve was performed in 4 patients. Three of the 4 patients in whom nerve reconstruction was performed regained satisfactory movement of their tongue. In the review of the literature, the mean patient age was 45.8 years. Patients presented with tongue atrophy (91.6%), headache (60.9%), and dysphagia (31.8%). The tumors were categorized as type A in 31.7% of these patients, type B in 38.6%, type C in 6.2%, and type D in 23.4%.

CONCLUSION: The extreme lateral infrajugular transcondylar-transtubercular exposure approach, which is a modification of the extreme lateral suboccipital approach, provides sufficient exposure for most intracranial dumbbell-shaped hypoglossal schwannomas. Hypoglossal nerve reconstruction using a sural nerve graft improves tongue atrophy and movement for patients with resected nerves.

Management of Anterolateral Foramen Magnum Meningiomas: Surgical Vs Conservative Decision Making

Neurosurgery 67[ONS Suppl 1]:ons00-ons00, 2010. DOI: 10.1227/01.NEU.0000382971.63877.DD

Anterolateral meningiomas of the foramen magnum (FMMs) represent a neurosurgical challenge because they grow in close contact with osteoarticular, nervous, and vascular structures that cannot be sacrificed or retracted. OBJECTIVE: To evaluate our strategy and results in 26 patients with FMMs and analyze factors affecting the decision-making process, resection, and outcome. METHODS: Among 26 consecutive symptomatic FMM (10 anterior, 16 lateral) patients (16 women, 10 men, ages 28-82 years), 4 older than 70 years of age were untreated. Twentytwo were operated on using a posterolateral approach, with the vertebral artery transposed in 19 and the occipital condyle drilled in 10. We analyzed the characteristics and outcome of untreated cases, the utility of THE occipital condyle drilled, the difficulties of microdissection, morbidity and total removal rates, the outcome of tumor residues, and the literature on radiosurgery. RESULTS: Three of 4 untreated patients remained clinically stable at 2 to 5 years. After systematic vertebral artery medial transposition and occipital condyle drilled in 6 cases, our technique evolved with experience in the next 16 (vertebral artery transposed in 13 of 16; occipital condyle drilled in 4 of 13) for dissecting anteriorly beyond midline (anterior FMMs). Retrocondylar access was sufficient for lateral FMMs. Tumors were totally removed in 16 of 22 (73%). One patient died, and 4 had permanent deficits. Follow-up of more than 5 years in 12 patients showed no C0-1 instability, and slight increase of tumor residue size 7 years after surgery. In the literature, 15 FMMs treated with radiosurgery are reported, 13 at diagnosis and 2 at recurrence, with short-term clinical and radiological safety and efficacy. CONCLUSION:We currently recommend (1) aiming for subtotal removal in difficult cases, (2) remaining conservative in asymptomatic or elderly patients with mild symptoms, and (3) considering radiosurgery at diagnosis for small (<30 mm) symptomatic FMMs or as an adjunct for evolving residues/recurrences in poor candidates for resection.