Microsurgical anatomy of the superior petrosal venous complex: new classifications and implications for subtemporal transtentorial and retrosigmoid suprameatal approaches

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Object

The purpose of this study was to define the patterns of drainage of the superior petrosal venous complex (SPVC) along the petrous ridge in relation to the Meckel cave and internal acoustic meatus (IAM) and to delineate its effect on the surgical exposures obtained in subtemporal transtentorial and retrosigmoid suprameatal approaches.

Methods

The patterns of drainage of the SPVC along the petrous ridge were characterized according to their relation to the Meckel cave and the IAM based on an examination of 30 hemispheres. Subtemporal transtentorial and retro-sigmoid suprameatal approaches were performed in three additional cadavers to demonstrate the effect of the drainage pattern on the surgical exposures.

Conclusions

The SPVC emptied into the superior petrosal sinus (SPS) within a distance of 1 cm from the midpoint of the Meckel cave. The patterns of drainage of the SPVC were classified into three groups. Type I emptied into the SPS above and lateral to the boundaries of the IAM. The most common type, Type II, emptied between the lateral limit of the trigeminal nerve at the Meckel cave and the medial limit of the facial nerve at the IAM, within an area of approximately 13 mm. Type III emptied into the SPS above or medial to the Meckel cave. The ideal SPVC for a subtemporal transtentorial approach (with or without anterior extradural petrosectomy) seems to be a Type I. In SPVC Type III and those Type II cases in which the SPVC is located near the Meckel cave, the amount of working space is significantly limited in a subtemporal transtentorial approach. In contrast, the ideal type of SPVC for a retrosigmoid suprameatal approach would be a Type III, and the SPVC must be divided in the majority of Type I and II cases for a satisfactory surgical exposure along the Meckel cave and middle fossa dura. The proposed modified classification system and its effect on the surgical exposure may aid in planning the approach directed along the petrous apex and may reduce the probability of venous complications.

Abbreviations used in this paper:CT = computed tomography; IAM = internal acoustic meatus; MR = magnetic resonance; SPS = superior petrosal sinus; SPVC = superior petrosal venous complex; V3 = mandibular division of the trigeminal nerve.

Article Information

Address reprint requests to: Necmettin Tanriover, M.D., Mehtap sok. Çiçek çikmazi. Ulasş Apt. No: 2/6, Caddebostan, Istanbul, Turkey 34728. email: nctan27@yahoo.com.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Photographs of cadaveric specimens obtained during stepwise dissection of the posterior surface of the right temporal bone. A: The cranial nerves and the terminal portion of the SPVC have been preserved in this dissection. The SPVC enters the superior petrosal sinus just lateral to the Meckel cave. The measurement from Point A to Point B was the distance between the midpoint of the roof of the Meckel cave and the point of entry of the SPVC into the superior petrosal sinus. The measurements from Point C to Point D and Point E to Point F were the distances from the medial and lateral limits of the trigeminal nerve at its point of entry at the Meckel cave to the terminal tips of the cisternal portions of the abducent and facial nerves, where these cranial nerves penetrated the clival dura mater and the IAM, respectively. The fourth cranial nerve entered the tentorium (Point G) an average distance of 7 mm from the midpoint of the roof of the Meckel cave (Point A). B: Enlarged view of the fundus of the Meckel cave. The width of the Meckel cave (Line H–I) was approximately 8 mm, and its height at the midpoint (Line J–K) averaged 3 mm. The width of the trigeminal nerve at the point of entry along the Meckel cave (Line L–M) was 5 mm. A. = artery; Bas. = basilar; CN = cranial nerve; Pet. = petrosal; Sup. = superior.

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    Drawings of the terminal part of the superior petrosal vein superimposed on photographs of a section of a cadaveric head along the posterior surface of the right temporal bone, representing the proposed classification of the SPVC. The cerebellum and the brainstem have been removed, and all of the cranial nerves of the region have been preserved to demonstrate three different patterns of drainage of the SPVC. A: In Type I (identified in 19% of the specimens), the SPVC empties into the SPS above or lateral to the IAM at a point lateral and superior to the medial limit of the facial nerve at its point of entry into the IAM. B: In Type II (72%), the SPVC empties into the SPS between the lateral limit of the trigeminal nerve at its point of entry into the Meckel cave and the medial limit of the facial nerve at its point of entry into the IAM, within a distance of approximately 13 mm. C: In Type III (9%), the SPVC empties into the SPS above or medial to the boundaries of the Meckel cave at a point medial to the lateral limit of the trigeminal nerve at its site of entry into the Meckel cave. Labyr. = labyrinthine; V2 = maxillary division of the trigeminal nerve. (Definitions of other abbreviations can be found in the legend to Fig. 1.)

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    Characteristics of the three types of drainage of the SPVC. A: A cadaveric dissection along the posterior surface of the left temporal bone. The cerebellum and the brainstem have been removed and the cranial nerves along with the premeatal segment of the anterior inferior cerebellar artery (AICA) have been preserved to demonstrate their relation with the terminal portion of the SPVC. The SPVC enters the SPS lateral to the IAM, at a point lateral and superior to the medial limit of the facial nerve at the IAM (SPVC Type I). B: Another specimen with an SPVC Type I, superolateral view. The middle fossa dura has been elevated and the cerebellum has been retracted to expose the posterior surface of the left temporal bone from above. The ninth, 10th, and 11th cranial nerves have been preserved and exposed. The SPVC enters the SPS lateral and superior to the facial nerve. C: A superior view of the posterior surface of the left temporal bone showing an SPVC Type II in another specimen. The tentorium, except for the edge, has been removed. The SPVC empties into the SPS between the lateral limit of the trigeminal nerve at its point of entry into the Meckel cave and the medial limit of the facial nerve at its point of entry into the IAM. The tributaries of the SPVC—the veins of the cerebellopontine fissure and middle cerebellar peduncle and the transverse pontine vein—have been preserved along with the cranial nerves of the region. D: A superior view of another example of an SPVC Type II, in which the SPVC drains into the SPS between the Meckel cave and the IAM. The SPS has been divided over the entrance of the Meckel cave to expose the trigeminal nerve along the porus of the cave. The cerebellum has been retracted to display the course of the tributaries of the SPVC and the cranial nerves. The transverse pontine vein drains the anterior part of the pons, then passes below the trochlear and trigeminal nerves to join the SPVC. Small anastomotic venous channels of the middle cerebellar peduncle arise in the region of the foramen of Luschka near the flocculus and ascend to join the SPVC. The vein of the cerebellopontine fissure passes medially to join the SPVC. E: An SPVC Type III and a superolateral view of the origin and course of the ninth, 10th, and 11th cranial nerves on the left side of the cadaveric head. The terminal part of the SPVC empties into the SPS above and medial to the boundaries of the Meckel cave (blue arrow). F: An SPVC Type III and a left-sided retrosigmoid exposure in another specimen. The cadaveric head was placed in a position simulating the three-quarter prone position. The SPVC drains into the SPS at a point above and medial to the lateral limit of the trigeminal nerve at its site of entry into the Meckel cave. G: An SPVC Type III and a combined supra- and infratentorial presigmoid exposure through a translabyrinthine approach on the left side in another specimen. The tentorium has been cut, and the cerebellum has been retracted to show the course and drainage pattern of the SPVC, which empties into the SPS above and medial to the Meckel cave, at a point medial to the lateral limit of the trigeminal nerve at the Meckel cave. H: A superolateral view of the posterior part of the left temporal bone in another specimen. The SPVC empties into the SPS as two separate stems. The SPVC Type I enters the SPS lateral to the IAM at a point lateral and superior to the medial limit of the facial nerve at the IAM. The SPVC Type II empties into the SPS between the lateral limit of the Meckel cave and the medial limit of the IAM. Cer. = cerebellar or cerebello-; Fiss. = fissure; Jug. = jugular; Mid. = middle; Ped. = peduncle; Pon. = pontine; SCA = superior cerebellar artery; Tent. = tentorium; Trans. = transverse; V. = vein; Vert. = vertebral. (Definitions of other abbreviations can be found in the legends to Figs. 1 and 2.)

  • View in gallery

    The effect of the pattern of drainage of the SPVC on the operative exposure during subtemporal transtentorial approaches with or without anterior petrosectomy. A–C: Stepwise dissection of a cadaveric specimen in a left subtemporal transtentorial approach. A: The inset shows the site of the scalp incision. The temporal lobe (Temp.) has been elevated to expose the tentorial incisura and the perimesencephalic cisterns. Two separate steps of the tentorial incision have been marked with interrupted blue lines. The first part of the tentorial incision begins at a point just behind the entry of the trochlear nerve along the tentorial edge, continues posterolaterally, and parallels the SPS. The second part is made perpendicular to the first and directed anterolaterally to the lateral edge of the trigeminal nerve towards V3. The portions of the tentorium that are highlighted in light orange, light yellow, and light red indicate the different sites along the SPS into which the SPVC empties in the Type I, Type II, and Type III drainage patterns, respectively, showing the effect the drainage patterns have on surgical exposure. The site of drainage is above or lateral to the IAM in SPVC Type I; between the lateral limit of the Meckel cave and the medial limit of the IAM in Type II; and medial to the Meckel cave in Type III. The ideal type of SPVC for a subtemporal transtentorial approach would be Type I, which provides at least 1 cm of extra space lateral to the Meckel cave to access the neighboring cisterns following the second part of the tentorial incision in the subtemporal approach. In the SPVC Type III specimens and some of the Type II specimens, the amount of working space is significantly limited during the subtemporal transtentorial approach (particularly when an extradural anterior petrosectomy is performed), and the exposure to the anterior surface of the pons is reduced. B: The initial part of the tentorial incision has been completed, revealing the terminal part of the SPVC. In this specimen, the amount of surgical exposure is limited by the SPVC Type III. C: The second part of the incision has been made perpendicular to the first and has traversed the SPS approximately at the lateral limit of the Meckel cave. The SPVC Type III has been transected to complete the tentorial division. D: A left-sided subtemporal transtentorial approach in another specimen. The first part of the incision, parallel to the SPS, has been completed, and two separate stems of the SPVC have been exposed. The SPVC Type II, located between the Meckel cave and the IAM, has a more limited effect on the surgical view, whereas the SPVC Type III substantially limits the surgeon's ability to obtain a sufficient surgical exposure. Ant. Ch. A. = anterior choroidal artery; C. = cerebral; Com. = communicating; I.C.A. = internal carotid artery; Olf. = olfactory; Ophth. = ophthalmic; P. = posterior; S.C.A. = superior cerebellar artery; Tr. = tract. (Definitions of other abbreviations can be found in the legends to Figs. 13.)

  • View in gallery

    The effect of the SPVC drainage pattern on surgical exposure during the retrosigmoid suprameatal approach. A–C: Posterior view through a left retrosigmoid craniotomy. Stepwise cadaveric dissection of a left retrosigmoid suprameatal approach. A: The cerebellum has been retracted to expose the neurovascular structures in the cerebellopontine angle. A large SPVC Type II courses above the suprameatal tubercle, the osseous prominence located above the porus of the IAM, and empties into the SPS just medial to the porus of the acoustic canal between the Meckel cave and the IAM. The inset shows the head position and the skin incision. B: The SPVC Type II empties into the SPS between the Meckel cave and the medial limit of the IAM. This drainage pattern was observed in 72% of the specimens. The posterior wall of the IAM has been removed and the cleavage planes between the facial nerve and the divisions of the vestibulocochlear nerve can be distinguished. The SPVC has been preserved during opening of the posterior wall of the IAM, but the SPVC Type II significantly blocks access to the suprameatal area and the region of the Meckel cave. The best surgical exposure for drilling the suprameatal tubercle is achieved in cases with an SPVC Type III, in which the petrosal vein empties into the SPS above or medial to the boundaries of the Meckel cave. The inset shows the drainage pattern of the SPVC in this specimen. C: The SPVC has been divided to obtain sufficient working area for drilling the suprameatal tubercle, which has been removed. The removal of the suprameatal tubercle provided additional exposure of the middle fossa dura mater along the trigeminal nerve at the porus of the Meckel cave. Coch. = cochlear; inf. = inferior; N. = nerve; S.C.A. = superior cerebral artery; Sig. = sigmoid; Vest. = vestibular. (Definitions of other abbreviations can be found in the legends to Figs. 14.)

  • View in gallery

    Three-dimensional CT angiograms and MR venograms demonstrating different SPVC drainage patterns. A and B: Three-dimensional CT angiograms obtained in the same patient, demonstrating an SPVC Type I. A: Posterior view of the left petroclival area. The SPVC empties into the left superior petrosal sinus above the IAM. B: Oblique view demonstrating the relationship between the point of entry of the SPVC and the IAM. C: A 3D CT angiogram obtained in another patient. Two separate SPVCs empty into the superior petrosal sinus. The SPVC Type I joins the superior petrosal sinus above and lateral to the IAM, and the SPVC Type II empties into the sinus between the trigeminal impression and the medial limit of the IAM. D and E: Posterosuperior and oblique views of venous phase 3D MR angiograms obtained in a patient with a left tentorial meningioma. The SPVC empties into the superior petrosal sinus anterior to the lesion and above the IAM. The tributaries that drain into the SPVC can be recognized better in the oblique view. Note that it is difficult to evaluate the pattern of drainage of the SPVC on the venous phase MR angiogram because the exact location of the IAM cannot be shown clearly. Ac. = acoustic; Impress. = impression; Int. = internal; Mea. = meatus; Sin. = sinus. (Definitions of other abbreviations can be found in the legends to Figs. 15.)

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