Introduction: We aimed to study the anatomical variations of the superior petrosal vein (SPV) complex (SPVC ) and to verify the balanced Fast Field Echo (bFFE) or equivalent sequences anatomical findings with corresponding surgical observations.

Methods: We reviewed all our trigeminal microvascular decompressions between September 2012 and July 2016. Preoperative bFFE and operative videos were studied and compared in the anatomical features of SPV and its direct tributaries. Statistical analysis was conducted.

Results: Fifty patients (mean age 67.18 years) were studied. Women and right sided operations accounted each for 58% of the patients. The applied imaging and operative anatomy of the SPVC was described. Twenty-nine different venous combinations were observed and classified into 3 major patterns and 10 sub-patterns according to the number of SPVs and the total direct tributaries in relation to the number of SPVs. The most common pattern was pattern 1 in 64%. Eighty percent of cases belonged to 4 sub-patterns. Type II drainage (Tanriover et al) into the SPS was predominant (85.7%). The vein of the cerebellopontine fissure(28.1%)and pontotrigeminal vein (26.8%)were the most frequent tributaries. At least one SPV (in 54%) and at least one direct tributary (90%) disturbed the operative field. The bFFE images showed a complete correlation with the intraoperative findings in 62% of cases. The reliability of bFFE had a significant correlation with a 3 Tesla magnets and higher pixel bandwidth. Sensitivity and specificity of bFFE were 93.7% and 95.2% for an SPV disturbing the operative field; 97.3% and 95% for a tributary disturbing the operative field; and 92.9% and 88% for predicting venous compression of the trigeminal nerve, respectively.

Conclusions: We suggested a system to classify the variations of SPVC into patterns and sub-patterns. Most SPVCs fall into four common sub-patterns. Good quality bFFE is an available powerful tool for assessing each individual SPVC anatomy preoperatively.

Patient Care: The variations of SPVC anatomy was not throughly studied in the literature. This study analyzed the exact vein combinations that formed different 50 SPVC. The huge different individual variations lead us to a more practical and easy to use classification based on the patterns of each SPVC (number of SPV(s)) and sub-patterns (number of the total direct tributaries of SPV(s)). This classification could give the neurosurgeon a key for a better appreciation of the individual SPVC anatomy before and during each cerebellopontine angle (CPA) operation. Furthermore, it promotes unifying our definition for each component of the SPVC (SPV(s) with all its tributaries), especially that unspecific terms or definitions of SPVC components are very commonly used in the literature (see Ref 1,8,11,12,17,19,21,24). Obviously, a unified nomenclature, which we emphasized based on previous well structured anatomical studies (Ref 14,20,23), can facilitate our communication regarding SPVC anatomy weather in clinical routine or in future research. The findings of this paper may facilitate the understanding of the exact venous drainage of individual SPVCs in further surgical or anatomical studies. It could also provide us a step forward toward understanding the, until yet, unpredictable individual complication risk resulting from SPVC injuries (Ref 1,9,11,12,13,21,22). Combining the assessment of the individual SPVC anatomy with the assessment of the remaining major venous drainage pathways in the posterior fossa (i.e. tentorial and galenic systems) may help to establish an individual preoperative model for predicting the safety of severing each component of a given SPVC.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the surgical significance of the SPVC anatomy 2) Appreciate the vast individual variations of SPVC anatomy and the possibility of individual preoperative assessment of each SPVC. 3) Identify the anatomical landmarks where each direct tributary of SPV, could be detected in the bFFE MRI or equivalent sequences, 4) Define each component of the SPVC intraoperatively, 5) Have an overview of the patterns and sub patterns of SPVC

References: 1. Anichini G, Iqbal M, Rafiq N, Ironside J, Kamel M: Sacrificing the superior petrosal vein during microvascular decompression. Is it safe? Learning the hard way. Case report and review of literature. Surg Neurol Int 7:S415-20, 2016 2. Ardeshiri A, Ardeshiri A, Linn J, Tonn J-C, Winkler P a: Microsurgical anatomy of the mesencephalic veins. J Neurosurg 106:894-899, 2007 3. Besta R: MRI 3D C ISS - A Novel Imaging Modality in Diagnosing Trigeminal Neuralgia - A Review. J Clin Diagnostic Res 10:1-3, 2016 4. Cheng L: Complications after obliteration of the superior petrosal vein: Are they rare or just underreported? J Clin Neurosci 31:1-3, 2016 5. Choudhari KA: Superior petrosal vein in trigeminal neuralgia. Br J Neurosurg 21:288-292, 2007 6. Docampo J, Gonzalez N, Munoz A, Bravo F, Sarroca D, Morales C: Neurovascular study of the trigeminal nerve at 3 T MRI. Neuroradiol J 28:28-35, 2015 7. Ebner FH, Roser F, Shiozawa T, Ruetschlin S, Kirschniak A, Koerbel A, et al: Petrosal vein occlusion in cerebello-pontine angle tumour surgery: An anatomical study of alternative draining pathways. Eur J Surg Oncol 35:552-556, 2009 8. Gharabaghi A, Koerbel A, Löwenheim H, Kaminsky J, Samii M, Tatagiba M: The impact of petrosal vein preservation on postoperative auditory function in surgery of petrous apex meningiomas. Neurosurgery 59(ONS Suppl 1):ONS68-74, 2006 9. Inamasu J, Shiobara R, Kawase T, Kanzaki J: Haemorrhagic venous infarction following the posterior petrosal approach for acoustic neurinoma surgery: A report of two cases. Eur Arch Oto-Rhino-Laryngology 259:162-5, 2002 10. Jannetta PJ, McLaughlin MR, Casey KF: Technique of microvascular decompression. Technical note. Neurosurg Focus 18(5):E5, 2005 11. Koerbel A, Gharabaghi A, Safavi-Abbasi S, Samii A, Ebner FH, Samii M, et al: Venous complications following petrosal vein sectioning in surgery of petrous apex meningiomas. Eur J Surg Oncol 35:773-779, 2009 12. Liebelt BD, Barber SM, Desai VR, Harper R, Zhang J, Parrish R, et al: Superior Petrosal Vein Sacrifice During Microvascular Decompression: Perioperative Complication Rates and Comparison with Venous Preservation. World Neurosurg 104:788-794, 2017 13. Masuoka J, Matsushima T, Hikita T, Inoue E: Cerebellar swelling after sacrifice of the superior petrosal vein during microvascular decompression for trigeminal neuralgia. J Clin Neurosci 16:1342-4, 2009 14. Matsushima K, Matsushima T, Kuga Y, Kodama Y, Inoue K, Ohnishi H, et al: Classification of the superior petrosal veins and sinus based on drainage pattern. Neurosurgery 10:357-367, 2014 15. Matsushima K, Ribas ESC, Kiyosue H, Komune N, Miki K, Rhoton AL: Absence of the superior petrosal veins and sinus: Surgical considerations. Surg Neurol Int 26:34, 2015 16. Matsushima T, Rhoton AL, de Oliveira E, Peace D: Microsurgical anatomy of the veins of the posterior fossa. J Neurosurg 59:63-105, 1983 17. Mclaughlin MR, Jannetta PJ, Clyde BL, Subach BR, Comey CH, Resnick DK: Microvascular decompression of cranial nerves: lessons learned after 4400 operations. J Neurosurg 90:1-8, 1999 18. Mizutani K, Toda M, Yoshida K: The Analysis of the Petrosal Vein to Prevent Venous Complications During the Anterior Transpetrosal Approach in the Resection of Petroclival Meningioma. World Neurosurg 93:175-182, 2016 19. Pathmanaban ON, O'Brien F, Al-Tamimi YZ, Hammerbeck-Ward CL, Rutherford SA, King AT: Safety of Superior Petrosal Vein Sacrifice During Microvascular Decompression of the Trigeminal Nerve. World Neurosurg 103:84-87, 2017 20. Rhoton ALJ: The Posterior Fossa Veins, in Rhoton AL (ed): The Posterior Cranial Fossa: Microsurgical Anatomy & Surgical Approaches. Vol 47. Philadelphia: Williams & Wilkins Co., 2000, pp S69-S92 21. Ryu H, Yamamoto S, Sugiyama K, Yokota N, Tanaka T: Neurovascular Decompression for Trigeminal in Elderly Patients. Neural Med Chir 39:226-230, 1999 22. Singh D, Jagetia A, Sinha S: Brain stem infarction: a complication of microvascular decompression for trigeminal neuralgia. Neurol India 54:325-6, 2006 (Letter) 23. Tanriover N, Abe H, Rhoton AL, Kawashima M, Sanus GZ, Akar Z: Microsurgical anatomy of the superior petrosal venous complex: new classifications and implications for subtemporal transtentorial and retrosigmoid suprameatal approaches. J Neurosurg 106:1041-1050, 2007 24. Watanabe T, Igarashi T, Fukushima T, Yoshino A, Katayama Y: Anatomical variation of superior petrosal vein and its management during surgery for cerebellopontine angle meningiomas. Acta Neurochir (Wien) 155:1871-1878, 2013 25. Yang YM, Wang ZW, Cui Z, Jiang HZ, Sha C, Yuan QG, et al: [Anatomy and management of superior petrosal vein in microvascular decompression for trigeminal neuralgia]. Zhonghua Yi Xue Za Zhi 21:522-524, 2017 (Chin) 26. Yoshino N, Akimoto H, Yamada I, Nagaoka T, Tetsumura A, Kurabayashi T, et al: Trigeminal Neuralgia: Evaluation of Neuralgic Manifestation and Site of Neurovascular Compression with 3D CISS MR Imaging and MR Angiography. Radiology 228:539-454, 2003