Day: July 3, 2026

Operative Neurosurgery 31:74–84, 2026

This study investigates the anatomical, radiological, and intraoperative relationships between the mastoid foramen (MF), mastoid emissary vein canal (MEVC), and mastoid air cell (MAC) pneumatization to improve planning and safety of the retrosigmoid approach (RSA). It reports measurements from cadaveric specimens, high-resolution CT of 100 patients, and surgical outcomes from 54 RSA procedures, linking MF/MEVC positions with pneumatization grades.

Key findings show the MF and MEVC are reliably posterior to MACs in most cases, with higher pneumatization grades correlated with shorter MF‑MAC and mMEVC‑MAC distances. Preoperative radiological assessment of these landmarks guided burr hole placement and border‑sealing techniques, reducing intraoperative MAC openings and postoperative complications.

Goal Assess whether the mastoid foramen (MF) and mastoid emissary vein canal (MEVC) can predict mastoid pneumatization and guide safer retrosigmoid approach (RSA) craniectomy planning.

Methods Combined anatomic dissection/drilling (2 dry temporal bones; 2 formalin-fixed heads), radiology (100 high‑resolution CTs; Han grade 1–4), and surgical review (54 RSA cases with complication tracking).

Classification & measures MF labeled “posterior” vs “anterior” to the most posterior mastoid air cell (MAC); MEVC labeled type 1 (posterior to MACs) vs type 2 (within MACs); quantified MF‑MAC distance and minimal MEVC‑MAC (mMEVC‑MAC) distance.

Key anatomy pattern MF was posterior to MACs in 99.4% of CT sides; MEVC was posterior to MACs in 88.0% (i.e., type 2 “within MACs” in the remainder).

Pneumatization relationships Higher Han pneumatization grades were associated with shorter MF‑MAC and mMEVC‑MAC distances (both P < .001), and these two distances were strongly correlated (r = 0.741, P < .001).

Age association Mastoid pneumatization grade decreased with age (inverse correlation, P < .001).

Surgical risk signal Intraoperative MAC opening occurred in 5.6% (3/54), and all had Han grade 4 pneumatization with type 2 MEVC (“within” MACs).

Clinical outcome No major intraoperative complications were reported; only one CSF wound leak (1.9%) occurred postoperatively and resolved with lumbar drainage.