Surgical Relevance of the Suprameatal Tubercle During Superior Petrosal Vein-Sparing Trigeminal Nerve Microvascular Decompression.

Background An enlarged suprameatal tubercle (SMT) can obscure visualization of the trigeminal nerve and require removal during microvascular decompression (MVD) surgery, especially when the superior petrosal vein (SPV) complex is preserved. Objective To define the incidence and important variables affecting the need for SMT removal with an SPV-sparing trigeminal nerve MVD. Methods Retrospective single-institution review identified patients who underwent a first-time, SPV-sparing MVD for trigeminal neuralgia (TGN) over a 26-mo period. SMT length (SMT-L), SMT width (SMT-W), and peri-trigeminal cerebellopontine cisternal thickness (CT) were measured from axial high-resolution magnetic resonance images. Need for SMT removal and use of endoscopic assistance was recorded. Data were analyzed using unpaired t-tests, and receiver operating characteristic (ROC)/area under the curve testing. Results A total of 43 MVD surgeries for TGN on 42 patients (mean age 52.7 ± 14.4 yr) were analyzed. Mean SMT-L, SMT-W, and CT were 9.8 ± 1.6, 2.0 ± 0.8, and 4.2 ± 1.5 mm, respectively. SMT removal via drilling was required in 4/43 cases (9.3%). Endoscopic assistance was used in 3 cases (2 SMT removed and 1 SMT preserved). SMT-W was the biggest predictor of the need for SMT removal on ROC analysis (area under the curve 0.97, 0.92-1.0 95% CI). The combined thresholds of SMT-W ≥ 3.2 mm and CT ≤ 3.5 mm demonstrated 100% sensitive and 100% specificity for the need to remove the SMT on optimal cutoff analysis. Conclusion SMT drilling is necessary in nearly 10% of SPV-sparing MVDs for TGN. The combination of SMT width and cerebellopontine cistern thickness is predictive of the need for SMT removal.