Individual variations of the superior petrosal vein complex and their microsurgical relevance in 50 cases of trigeminal microvascular decompression

Abstract

Background: We investigated the understudied anatomical variations of the superior petrosal vein (SPV) complex (SPVC), which may play some role in dictating the individual complication risk following SPVC injury.

Methods: Microvascular decompressions of the trigeminal nerve between September 2012 and July 2016. All operations utilized an SPVC preserving technique. Preoperative balanced fast field echo (bFFE) magnetic resonance imaging, or equivalent sequences, and operative videos were studied for individual SPVC anatomical features.

Results: Applied imaging and operative SPVC anatomy were described for fifty patients (mean age, 67.18 years; female sex and right-sided operations, 58% each). An SPVC component was sacrificed intentionally in 6 and unintentionally in only 7 cases. Twenty-nine different individual variations were observed; 80% of SPVCs had either 2 SPVs with 3 or 1 SPV with 2, 3, or 4 direct tributaries. Most SPVCs had 1 SPV (64%) and 2 SPVs (32%). The SPV drainage point into the superior petrosal sinus was predominantly between the internal auditory meatus and Meckel cave (85.7% of cases). The vein of the cerebellopontine fissure was the most frequent direct tributary (86%), followed by the pontotrigeminal vein in 80% of SPVCs. Petrosal-galenic anastomosis was detected in at least 38% of cases. At least 1 SPV in 54% of the cases and at least 1 direct tributary in 90% disturbed the operative field. The tributaries were more commonly sacrificed.

Conclusions: The extensive anatomical variation of SPVC is depicted. Most SPVCs fall into 4 common general configurations and can usually be preserved. BFFE or equivalent sequences remarkably facilitated the intraoperative understanding of the individual SPVC in most cases.

Keywords: Anatomy; Cerebellopontine angle; Microvascular decompression; Superior petrosal vein; Surgical anatomy; Trigeminal neuralgia.

Fig. 1

a A case of a left-sided MVD in a patient with an SPVC configuration of 1 SPV and 4 tributaries (1.4.) The SPV is formed by the confluence of the PTv and TPv. Note that the v.CPF and the ALMv join later at a more proximal point of the SPV. The v.CPF comes from the suprafloccular area at the cerebellopontine fissure. The flocculus is not exposed here, but the VII/VIII group indicates its location. The v.CPF has a lateral relation to the VII/VIII. The PTv comes into the operative field from a rostral direction. The TPv merges into our view from the medial and ventral aspect of the pons. b An axial bFFE slice from the same patient in a showing all 4 tributaries of the SPV intraoperatively. The PTv (only the very proximal tip is seen on this slice) and the TPv appear here, forming the SPV. The v.CPF and ALMv drain into the SPV more proximally. Interestingly, MRI also detected the TPv traversing through the TG rootlets. c A case of 3 huge direct tributaries on the right side obscuring the operative field completely. The SPV is very short and is barely seen. All 3 veins unite at one point to form the SPV. Note that the relationship between the veins usually could not be determined at their proximal cisternal parts. The bFFE reveals a second SPV formed by a PTv. Nevertheless, it could not be seen intraoperatively because of its medial course and field disturbance by the huge SPVC. d The same case as in c. After retracting the cerebellar edge, the distal parts of the tributaries on the pontine surface as well as their relations could be exposed. The v.CPF courses typically lateral to the v.MCP. e In this example of a left-sided CPA, the SPVC is causing less interference with the surgical corridor. The v.MCP is medial to the v.CPF and courses medially to VII/VIII. The SPV ends at a point between the TG and VII/VIII (drainage type II), although the angle of view is not ideal for this purpose. f Another example of a right CPA showing the PTv as an indirect tributary, which drains into ALMv at the pontine surface. This patient had 2 SPVs but only one of them appears here. ALMv anterior lateral marginal vein, bFFE balanced fast field echo, CPA cerebellopontine angle, MVD microvascular decompression, P petrous bone, PTv pontotrigeminal vein, SPV superior petrosal vein, SPVC superior petrosal vein complex, SPV2 second SPV, T tentorium, TG trigeminal nerve, TPv transverse pontine vein, v.CPF vein of cerebellopontine fissure, v.MCP vein of the middle cerebellar peduncle, VII/VIII seventh and eighth cranial nerves, asterisk Teflon sponge

Fig. 2

Type of SPV drainage into the SPS according to Tanriover et al. [31] a Type I drainage of the SPV into the SPS. b Type II drainage. c Type III drainage. SPS superior petrosal sinus, SPV superior petrosal vein, V trigeminal nerve, VII/VIII seventh and eighth cranial nerves

Fig. 3

a Right-sided CPA showing 2 SPVs and a total of 3 direct tributaries. There is an overall moderate disturbance of the operative field. b Same case presented in Fig. 1a. The distal part of ALMv courses over the anterior edge of the cerebellar surface. It is the most lateral tributary of the SPV. c A coronal bFFE image showing the left v.CPF at its origin at the suprafloccular cistern, ascending over the cerebellopontine fissure toward the SPV. The PTv here has a proximal horizontal part and could be mistaken in this image for the TPv. However, scrolling through the images revealed a typical course of the PTv. d An axial cut from aright CPA showing the v.MCP running over the middle cerebellar peduncle. The v.CPF is above the flocculus. ALMv anterior lateral marginal vein, bFFE balanced fast field echo, CPA cerebellopontine angle, F flocculus, PTv pontotrigeminal vein, SCA superior cerebellar artery, SPV superior petrosal vein, SPV1 first superior petrosal vein, SPV2 second superior petrosal vein, TG trigeminal nerve, TPv transverse pontine vein, v.CPF vein of cerebellopontine fissure, v.MCP vein of the middle cerebellar peduncle

Fig. 4

a An axial bFFE cut showing the left PTv leaving the lateral pontine sulcus to drain into the SPV. b A closer view from the same case of Fig. 1a showing the TPv traversing the trigeminal nerve. c Right-sided CPA showing 3 SPVs with 3 direct tributaries. This SPVC causes only minimal disturbance of the operative field. d A coronal bFFE cut showing the left PTv (lower arrow) and basal vein of Rosenthal (upper arrow) pointing to each other. Further scrolling of the images showed that they anastomose. e An axial bFFE cut showing the left TPv with its horizontal course originating at the ventral pons. f An axial bFFE cut at a lower level of the posterior fossa showing the left ALMv running over the anterior lateral edge of the cerebellar surface. ALMv anterior lateral marginal vein, bFFE balanced fast field echo, CPA cerebellopontine angle, PTv pontotrigeminal vein, SPV superior petrosal vein, SPVC superior petrosal vein complex, TG trigeminal nerve, TPv transverse pontine vein, v.CPF vein of cerebellopontine fissure, v.MCP vein of the middle cerebellar peduncle, VII/VIII seventh and eighth cranial nerves

Fig. 5

The 3 main patterns of an SPVC. a An SPVC with a single SPV. The general configuration here is 1 SPV with 3 tributaries, which was the most common SPVC configuration in the whole sample. b An SPVC with 2 SPVs. The configuration here is 2 SPVs with 3 tributaries, which was along with the configuration of 1 SPV with 2 tributaries, the second most common in the sample. c An SPVC with 3 SPVs. ALMv anterior lateral marginal vein, PTv pontotrigeminal vein, SPS superior petrosal sinus, SPV superior petrosal vein, , SPVC superior petrosal vein complex, SPV1 first superior petrosal vein, SPV2 second superior petrosal vein, SPV3 third superior petrosal vein, TPv transverse pontine vein, v.CPF vein of cerebellopontine fissure, v.MCP vein of the middle cerebellar peduncle, V trigeminal nerve, VII/VIII seventh and eighth cranial nerves

Fig. 6

A case of right-sided CPA with 2 different doubled SPV’s tributaries. a An intraoperative retrosigmoid view showing the SPV composed of a PTv1 and v.MCP, and ALMv1 joined the SPV at a more proximal point. A Teflon pad appears in the background. b View from a slightly different angle showing a second ALMv (ALMv2) as draining into a PTv2, which did not drain into the SPV. c, d Correspondent findings in bFFE axial views. Note that the v.MCP appeared in other slices, which are not shown here. Additionally, further bFFE slices show that the PTv2 drains directly into the vein of Rosenthal in this case without being part of the SPVC. ALMv1 fist anterior lateral marginal vein, ALMv2 second anterior lateral marginal vein, bFFE balanced fast field echo, CPA cerebellopontine angle, PTv1 first pontotrigeminal vein, PTv2 second pontotrigeminal vein, SCA superior cerebellar artery, SPV superior petrosal vein, SPVC superior petrosal vein complex, v.MCP vein of the middle cerebellar peduncle

Fig. 7

A case of right-sided CPA. a Axial bFFE magnetic resonance imaging showing an SPV1 composed of an ALMv and a PTv. b Another axial section showing an SPV 2 as the continuation of the v.MCP as well as an SPV 3 as a continuation of an TPv. c, d Corresponding intraoperative photographs of the same case. We can see here all the above described SPVC components, except the SPV 3 and its single tributary (TPv). This is because of the very medial course of the TPv and medial type III drainage of the SPV 3 into the SPS beyond the microsurgical field. ALMv anterior lateral marginal vein, bFFE balanced fast field echo, CPA cerebellopontine angle, SCA superior cerebellar artery, SPV superior petrosal vein, SPVC superior petrosal vein complex, SPV1 first SPV, SPV2 second SPV, SPV3 third SPV, TG trigeminal nerve, TPv transverse pontine vein, v.CPF vein of cerebellopontine fissure, v.MCP vein of the middle cerebellar peduncle

Fig. 8

A sketch representing, from left to right, Figs. 1c, 3a, and 4c, which has 1, 2, and 3 main SPVs, respectively. Each of them had a total of 3 tributaries. The incidence of operative field disturbance by more than 1 tributary (shown as percentages) is related inversely with the number of SPVs present (as the green arrow demonstrates). The red arrows demonstrate the number of tributaries converging into an SPV. SPV superior petrosal vein