Fig. 2.1
Three neurovascular complexes. (a) The upper complex includes the SCA, midbrain, superior cerebellar peduncle, cerebellomesencephalic fissure, tentorial cerebellar surface, and CNs III–V. The middle complex includes the AICA, pons, middle cerebellar peduncle, cerebellopontine fissure, petrosal surface, and CNs VI–VIII. The lower complex includes the PICA, medulla, inferior cerebellar peduncle, cerebellomedullary fissure, suboccipital surface, and CNs IX–XII. The SCA is divided into four segments: anterior pontomesencephalic (green), lateral pontomesencephalic (orange), cerebellomesencephalic (blue), and cortical (red). Each segment may be composed of one or more trunks, depending on the level of bifurcation of the main trunk. The AICA is divided into four segments: anterior pontine (green), lateral pontomedullary (orange), flocculonodular (blue), and cortical (red). The PICA is divided into five segments: anterior medullary (green), lateral medullary (orange), tonsillomedullary (blue), telovelotonsillar (yellow), and cortical (red) (Reprint with permission from Rhoton (2000a)). (b) The cerebellopontine fissures are V-shaped fissures formed where the cerebellum wraps around the pons and the middle cerebellar peduncles. These fissures have a superior and an inferior limb, which meet at a lateral apex. The cerebellopontine fissure is continuous with the cerebellomesencephalic fissure superiorly and cerebellomedullary fissure inferiorly. The petrosal fissure extends laterally from the apex of the cerebellopontine fissures. CN V arises from the lateral part of the pons near the point where the superior limb of the cerebellopontine fissure meets the cerebellomesencephalic fissure. CNs VII and VIII arise at the lateral end of the pontomedullary sulcus immediately rostral to the foramen of Luschka and choroid plexus and ventral to the flocculus. CNs IX–XI arise as a line of rootlets that exit the medulla along the posterior edge of the olive in the postolivary sulcus, ventral to the lateral edge of the cerebellomedullary fissure (Reprint with permission from Rhoton (2000c)). (c) Posterior view of the cranial base with CNs and arteries preserved. CN V enters into Meckel’s cave, CNs VII and VIII enter into the internal acoustic meatus, and CNs IX–XI enter into the jugular foramen. The SCA arises from the basilar artery near the apex at the midbrain level and passes below CNs III and IV and above CN V. The AICA originates from the basilar artery and encircles the pons near CNs VI–VIII. In most cases, the AICA passes below CNs VII and VIII, as seen in this specimen, but it may also pass above or between these nerves. The PICA arises from the vertebral artery at the upper medullary level and passes posteriorly around the medulla, coursing rostral to or between CNs IX and XI. There is slight asymmetry in the level of origin of the AICAs and marked asymmetry in the level of the origin of the PICAs, as is common (Reprint with permission From Rhoton (2000c)). (d) Both SCAs arise anterior to the midbrain and loop downward to the level of the junction of CN V with the pons. The right AICA reaches the superior surface of CN VII at its exit, and the left AICA reaches the inferior surface of CN VII at its brainstem exit. The AICA reapproaches CNs VII and VIII near the internal acoustic meatus where it sends the nerve-related branches. The right PICA arises from the vertebral artery at the medullary level and loops upward toward CNs IX and X (Reprint with permission from Rhoton (2013)). (e) The cerebellum has been removed to show the fourth ventricle, three cerebellar arteries, and CNs V and VII–XII. The fourth ventricle sits on the posterior surface of the pons and medulla. The flocculus projects laterally into the CPA (Reprint with permission from Rhoton (2007)). A artery, A.I.C.A. anterior inferior cerebellar artery, Bas. basilar, Cer. cerebello, Chor. Plex. choroid plexus, CN cranial nerve, Fiss. fissure, Flocc. flocculus, Inf. inferior, Med. medullary, Mes. mesencephalic, P.C.A. posterior cerebral artery, P.I.C.A. posterior inferior cerebellar artery, Ped. peduncle, Pet. petrosal, Pon. pontine, ponto, Quad. quadrangular, S.C.A. superior cerebral artery, Sulc. sulcus, Sup. superior, V. vein, Vert. vertebral
2.2 Upper Neurovascular Complex and Trigeminal Neuralgia
The upper neurovascular complex includes the SCA, midbrain, cerebellomesencephalic fissure, superior cerebellar peduncle, tentorial surface of the cerebellum, and CNs III–V. The SCA arises in front of the midbrain and passes below CNs III and IV and above CN V to reach the cerebellomesencephalic fissure, where it runs on the superior cerebellar peduncle and terminates by supplying the tentorial surface of the cerebellum (Rhoton 2013).
2.2.1 Anatomy of CN V
CN V arises from the lateral part of the pons and runs obliquely upward toward the petrous apex (Fig. 2.2). It exits the posterior fossa to enter the middle cranial fossa by passing forward beneath the tentorial attachment and through Meckel’s cave, which sits in the trigeminal impression on the upper surface of the petrous part of the temporal bone (Fig. 2.2a). Throughout the interval from the ganglion to the junction with the pons, the third-division fibers remain in a caudolateral position, second-division fibers in an intermediate position, and first-division fibers in a rostromedial position (Fig. 2.2c) (Emmons and Rhoton 1971). There are anastomoses between the fibers from each division in the area posterior to the ganglion. The cross section of the sensory root between the pons and the petrous apex is elliptical. In most cases, the angle between the longest diameter of this cross section and the longitudinal axis of the body of CN V is 40–50°, but can vary from 10 to 80° (Fig. 2.2d) (Gudmundsson et al. 1971).
Fig. 2.2
Lateral views, right CN V. (a) Meckel’s cave, the cistern that extends forward from the posterior fossa along CN V to the level of the midportion of the ganglion, has been exposed by removing the lateral dural wall of the cave. The motor root arises rostral to the sensory root and passes through Meckel’s cave on the medial side of the sensory root and ganglion (Reprint with permission from Rhoton (2000b)). (b) Four motor rootlets, which arise around the rostral margin of the sensory root, have been elevated to expose the anastomoses between the motor and sensory roots. The cerebellar lip projects forward to form the cerebellomesencephalic fissure and may hide the junction of the sensory root with the pons in the retrosigmoid approach (Reprint with permission from Rhoton (2000b)). (c) A cleavage plane between the three trigeminal divisions has been started anteriorly and extended backward to the level of the posterior root. The first-division fibers are rostromedial within the posterior root and the third-division fibers caudolateral with the second division being in an intermediate location (Reprint with permission from Rhoton (2000b)). (d) Variability of the longest axis of the elliptical cross section of CN V at the pons (broken line) to the longitudinal axis of the body (solid line). The long axis of most nerves makes a 40–50° angle with the longitudinal axis of the body (A); however, this can vary from 10° (C) to 80° (B). In (b) the third division is almost directly lateral to the first division, and in c it is almost directly caudal (Reprint with permission from Gudmundsson et al. (1971)). CN cranial nerve, Cer. cerebellar, Gang. ganglion. V1 the first trigeminal nerve division, V2 the second trigeminal division, V3 the third trigeminal nerve division
At the junction of the nerve with the pons, as many as 15 motor or aberrant sensory roots may be spread around the rostral half of the junction of the main sensory cone with the pons (Fig. 2.2b) (Gudmundsson et al. 1971). The aberrant sensory fibers penetrate the pons around the rostral two-thirds of the main sensory root and usually join the root a short distance from the brainstem. Of 66 aberrant rootlets found in our previous study of 50 specimens, 49 joined the first division, ten the second division, and seven the third division (Gudmundsson et al. 1971). Motor rootlets also arise around the rostral part of the nerve as 4–14 separate rootlets; however, they tend to arise further from the brainstem exist zone of the sensory root than the accessory sensory rootlets (Gudmundsson et al. 1971). Anastomoses between the motor and sensory roots are present in most nerves.
2.2.2 Anatomy of the SCA
The SCA arises in front of the midbrain, usually from the basilar artery near the apex, and passes below CN III, but may infrequently arise from the proximal posterior cerebral artery and pass above CN III (Fig. 2.3). It dips caudally and encircles the brainstem near the pontomesencephalic junction, passing below CN IV and above CN V. Its proximal portion courses medial to the free edge of the tentorium cerebelli, and its distal part passes below the tentorium (Fig. 2.3a). A meningeal branch occasionally originates from the main or rostral trunk near where the artery passes under the tentorium and enters the free edge of the tentorium. The SCA usually arises as a single trunk and bifurcates into two major trunks, rostral and caudal, near CN V. About half of the SCAs have a point of contact with CN V, which is usually on the superior or superomedial aspect of the nerve (Fig. 2.3d) (Hardy and Rhoton 1978). Depending on the site of bifurcation, the SCA trunk reaching the nerve may be the main, rostral, caudal, or both the rostral and caudal trunks, or a marginal hemispheric branch. After passing above CN V, the artery enters the cerebellomesencephalic fissure where its branches give rise to perforating branches to the brainstem and cerebellar peduncles and to precerebellar arteries entering the deep cerebellar white matter and dentate nucleus. On leaving the cerebellomesencephalic fissure, its branches pass posteriorly under the tentorial edge and are distributed to the tentorial cerebellar surface. The rostral trunk supplies the vermian and paravermian areas, and the caudal trunk supplies the hemispheric part of the tentorial surface.
Fig. 2.3
Superior cerebellar artery. (a) Superior view. The SCA arises from the basilar artery anterior to the midbrain and encircles the pontomesencephalic junction to enter the cerebellomesencephalic fissure. It usually courses below CNs III and IV and above V and bifurcates into two major trunks, rostral and caudal, near CN V. The rostral trunk supplies the vermian and paravermian areas, and the caudal trunk supplies the hemisphere on the tentorial surface (Reprint with permission from Rhoton (2000a)). (b) Superolateral view. The right SCA arises from the basilar artery as a duplicate artery. The rostral duplicate trunk gives rise to vermian branches, and the caudal duplicate trunk gives rise to hemispheric branches, similar to the distribution of the rostral and caudal trunks formed by the bifurcation of a single SCA. The SCA or its major trunks often make a caudal loop to reach CN V ventral to the nerve. The superior petrosal vein and its tributaries also course near CN V. A well-developed pontotrigeminal vein, connecting the lateral mesencephalic vein with the superior petrosal vein, courses above the nerve (Reprint with permission from Rhoton (2000a)). (c) Right CPA. A large superior petrosal vein with multiple tributaries, including the pontotrigeminal and transverse pontine veins and the vein of the cerebellopontine fissure, passes above CN V. The AICA passes laterally between CNs VII and VIII and turns medially to course along the middle cerebellar peduncle and cerebellopontine fissure (Reprint with permission from Rhoton (2007)). (d) Superolateral view. SCA with an early bifurcation. The rostral trunk loops downward and indents the upper surface of CN V (Reprint with permission from Rhoton (2000b)). A. artery, A.I.C.A. anterior inferior cerebellar artery, Ant. anterior, Bas. basilar, Caud. caudal, Cer. cerebellar, cerebello, CN cranial nerve, Fiss. fissure, Hem. hemispheric, Lat. lateral, Mes. mesencephalic, Pet. petrosal, petrous, Pon. pontine, ponto, Rost. rostral, S.C.A. superior cerebral artery, Sup. superior, Tent. tentorial, Tr. trunk, Trans. transverse, Trig. trigeminal, V. vein
2.2.3 Anatomy of the Superior Petrosal Vein
The superior petrosal veins empty into the superior petrosal sinus as one to three bridging veins (Fig. 2.4) (Rhoton 2000e). This superior petrosal venous complex is among the largest in the posterior fossa. It is frequently encountered in approaches to CN V and occasionally compresses CN V. The superior petrosal veins are usually formed by the union of several veins. The most common tributaries of the superior petrosal veins are the transverse pontine, pontotrigeminal, and anterolateral marginal veins and the veins of the cerebellopontine fissure and middle cerebellar peduncle (Matsushima et al. 1983, 2014). Of 20 superior petrosal sinuses examined in our previous study, eight received one superior petrosal vein, ten received two, and two received three (Matsushima et al. 1983). The draining points of the superior petrosal vein into the superior petrosal sinus were classified into medial, intermediate, or lateral groups based on whether they drained into the superior petrosal sinus in an intermediate location above the internal acoustic meatus or medial or lateral to the meatus. Of 34 superior petrosal veins, 22 (64.7 %) were of the medial type, three (8.8 %) were of the intermediate type, and nine (26.5 %) were of the lateral type (Matsushima et al. 1983).
Fig. 2.4
Posterior fossa veins. (a) CN V may be compressed by the superior petrosal veins and their tributaries, including the transverse pontine and pontotrigeminal veins and the veins of the cerebellopontine fissure and middle cerebellar peduncle. The right transverse pontine vein makes contact with the lower surface of the right CN V, and the left transverse pontine vein compresses the upper surface of the left CN V. The vein of the pontomedullary sulcus or the middle cerebral peduncle may compress CN VII, as seen in both sides of this specimen. CNs IX and often X may be compressed by surrounding veins, such as the bridging veins emptying into the jugular foramen or the vein of the pontomedullary sulcus, as seen on the right side (Reprint with permission from Rhoton (2000e)). (b) Superolateral view. A large superior petrosal vein formed by the union of the transverse pontine, pontotrigeminal, and anterolateral marginal veins and the vein of the cerebellopontine fissure. The superior surface of CN V is indented by the transverse pontine and pontotrigeminal veins. The SCA bifurcates into rostral and caudal trunks medial to CN V (Reprint with permission from Rhoton (2000e)). (c) The veins in the posterior fossa are divided into three groups: a galenic group (green) that drains into the vein of Galen, a petrosal group (blue) that drains into the superior and inferior petrosal sinuses, and a tentorial group that drains into the sinuses near the torcula. The veins surrounding CN V, VII, or IX and X, may be associated with trigeminal neuralgia, hemifacial spasm, or glossopharyngeal neuralgia, respectively (Reprint with permission from Rhoton (2000e)). Ant. anterior, Bas. basal, Br. Bridg. bridging, Caud. caudal, Cer. cerebellar, cerebello, cerebral, CN cranial nerve, Com. communicating, Fiss. fissure, For. foramen, He. hemispheric, Inf. inferior, Int. internal, Jug. jugular, Lat. lateral, Marg. marginal, Med. medial, medullary, Mes. mesencephalic, Mid. middle, Ped. peduncle, peduncular, Pet. petrosal, Pon. pontine, ponto, Post. posterior, Retro–oliv. retro-olivary, Rost. rostral, S.C.A. superior cerebral artery, Sulc. sulcus, Sup. superior, Tr. trunk, Trans. transverse, Trig. trigeminal, V. vein
2.2.4 Offending Vessels of Trigeminal Neuralgia
The SCA, AICA, PICA, the superior petrosal vein and its tributaries, or any combination of these vessels may cause compression of CN V (Figs. 2.5, 2.6, 2.7, and 2.8) (Apfelbaum 2000; Barker et al. 1996; Hong et al. 2011; Jannetta 1980; Li et al. 2004; Lorenzoni et al. 2008; Matsushima et al. 2004; Sekula et al. 2009; Sindou et al. 2008; Thomas and Vilensky 2014). The vertebral and basilar arteries have rarely been reported to be the compressing vessel (Apfelbaum 2000; Barker et al. 1996; Lorenzoni et al. 2008; Thomas and Vilensky 2014; Yang et al. 2012).
Fig. 2.5
Arterial compression of CN V. Sites of arterial compression of CN V. Orientation as shown in the central diagram. (a) Central diagram. The right CN V is compressed by a tortuous basilar artery, and the left CN V is compressed by the main trunk of the SCA. (b) The SCA bifurcates into rostral and caudal trunks prior to reaching CN V. The nerve is compressed by the caudal trunk. (c) The SCA bifurcates distal to the nerve. The nerve is compressed by the main trunk. (d) The SCA bifurcates prior to reaching the nerve. The nerve is compressed by both the rostral and caudal trunks. (e) The nerve is compressed by a large pontine artery. (f) The nerve is compressed by an AICA that has a high origin and loops upward into the medial surface of the nerve (Reprint with permission from Rhoton (1990)). A. artery, A.I.C.A. anterior inferior cerebellar artery, Bas. basilar, Ca. caudal, Ro. rostral, S.C.A. superior cerebral artery, Tr. trunk
Fig. 2.6
Arterial compression of CN V. Sites of arterial compression of CN V as seen through a suboccipital craniotomy. (a) Central diagram. The site of the skin incision (solid line) and the craniotomy (interrupted line), exposing the junction of the sigmoid and transverse sinuses, are shown in the inset. The cerebellum has been elevated to expose the junction of CN V with the pons. CN IV is at the superior margin of the exposure and CNs VII and VIII are at the lower margin. CN V is compressed by a loop of the SCA that dangles down into the axilla of the nerve. The site of compression on the artery is at the junction of the main trunk with the rostral and caudal trunks. (b) The nerve is compressed by the caudal trunk. (c) The nerve is compressed by the main trunk. (d) Compression by both the rostral and caudal trunks. (e) Compression by a pontine branch of the basilar artery. (f) Compression by the AICA from the inferior side. (g) Compression by a tortuous basilar artery from the medial side (Reprint with permission from Rhoton (1990)). A. artery, A.I.C.A. anterior inferior cerebellar artery, Bas. basilar, Ca. caudal, Ro. rostral, S.C.A. superior cerebral artery, Sup. superior, Tr. trunk
Fig. 2.7
Venous compression of CN V. Sites of venous compression of CN V. (a) Central diagram. The veins that commonly compress CN V are tributaries of the superior petrosal veins. The tributaries that converge on and may compress the nerve are the transverse pontine and pontotrigeminal veins and the veins of the cerebellopontine fissure and middle cerebellar peduncle. The transverse pontine veins course transversely across the pons. The vein of the middle cerebellar peduncle arises in the region of CNs VII and VIII and ascends on the pons. The vein of the cerebellopontine fissure arises along the superior limb of the cerebellopontine fissure. The pontotrigeminal vein arises on the upper pons and passes above CN V. (b) A transverse pontine vein compresses the lateral side of the nerve and joins the veins of the middle cerebellar peduncle and cerebellopontine fissure to empty into a superior petrosal vein. (c) The medial side of the nerve is compressed by a tortuous transverse pontine vein. (d) The lateral side of the nerve is compressed by the junction of the transverse pontine vein with the veins of the middle cerebellar peduncle and the cerebellopontine fissure. (e) The nerve is compressed on the medial side by the vein of the middle cerebellar peduncle and on the lateral side by the vein of the cerebellopontine fissure. (f) The lateral side of the nerve is compressed by the vein of the cerebellopontine fissure (Reprint with permission from Rhoton (1990)). Cer. cerebellar, cerebello, Fiss. fissure, Mid. middle, Ped. peduncle, Pon. pontine, ponto, Sup. superior, Trans. transverse, Trig. trigeminal, V. vein
Fig. 2.8
Venous compression of CN V. Sites of venous compression of CN V as seen through a retrosigmoid craniotomy. (a) The inset shows the site of the scalp incision (solid line) and the craniotomy (interrupted line). The superior petrosal veins empty into the superior petrosal sinus. CN V is compressed by the junction of a transverse pontine vein and the vein of the middle cerebellar peduncle with the superior petrosal vein. The vein of the cerebellopontine fissure ascends behind the nerve, and the pontotrigeminal vein passes above the nerve. (b) CN V is compressed on its medial side by a transverse pontine vein and on its lateral side by the vein of the middle cerebellar peduncle. (c) The lateral side of the nerve is compressed by a transverse pontine vein. (d) The medial side of the nerve is compressed by the junction of a transverse pontine vein with the veins of the middle cerebellar peduncle and cerebellopontine fissure. (e) The lateral side of the nerve is compressed by the junction of the transverse pontine vein with the veins of the middle cerebellar peduncle and cerebellopontine fissure. (f) The medial side of the nerve is compressed by the vein of the middle cerebellar peduncle. (g) The lateral side of the nerve is compressed by the vein of the cerebellopontine fissure (Reprint with permission from Rhoton (1990)). Cer. cerebellar, cerebello, Fiss. fissure, Mid. middle, Ped. peduncle, Pon. pontine, ponto, Sig. sigmoid, Sup. superior, Trans. transverse, Trig. trigeminal, V. vein
The most commonly found offending vessel found in vascular decompression operations for trigeminal neuralgia is the caudal loop of the SCA (Hardy and Rhoton 1978). The SCA was found to be compressing CN V in 52 % of the 50 CPAs that we previously examined and the AICA in 8 % (Hardy and Rhoton 1978). The point of contact between CN V and the SCA is usually on the superior or superomedial aspect of the nerve, and often a few fascicles of the nerve are distorted by an SCA that has looped down into the axilla between the medial side of the nerve and the pons. An arterial loop in the axilla may not be visible from the retrosigmoid view behind CN V if the SCA courses around the brainstem directly in front of the nerve, or if it passes over the rostral aspect of the nerve very close to the brainstem, where it may be hidden by the overhanging lip of the cerebellomesencephalic fissure. Exposure directed along the petrosal cerebellar surface, as in the common retrosigmoid approach, but also through the lateral part of the tentorial cerebellar surface, described as the infratentorial lateral supracerebellar approach, may provide better visualization of an arterial loop directly medial to the nerve (Fujimaki and Kirino 2000; Matsushima et al. 1989). The loop of the SCA may be seen dangling below the lower margin of the nerve, although it is not visible above the nerve. These SCA loops, however, always pass along the medial and rostral surfaces of the nerve to reach the cerebellomesencephalic fissure. This arterial loop may contact CN V more than once, especially if the loop is long enough to overlap. The medial axilla of the nerve must be carefully examined before concluding that there is no arterial loop in the axilla of the nerve. It is important to remember that the trunks do not pass directly from the side of the brainstem to the superior surface of the cerebellum, but, rather, that they dip into the deep fissure between the cerebellum and midbrain at the posterior margin of CN V. The most common site of compression of CN V on the SCA is around the junction of the main trunk with the origin of the rostral and caudal trunks (Rhoton 1990). However, other sites of compression are seen depending on how far distal the artery bifurcates in relation to CN V. If the SCA bifurcates near the basilar artery or if there is a duplicate configuration in which the rostral and caudal trunks arise directly from the basilar artery, both trunks may loop down into the axilla between the pons and CN V to compress the nerve. There are cases in which both the rostral and caudal trunks contact the nerve, so careful attention is needed to the caudal trunk to determine if it is compressing the junction of the nerve with the pons, which could be hidden by the overhanging lip of the cerebellomesencephalic fissure. Alternatively, if the artery bifurcates before reaching the nerve, the caudal trunk may compress the nerve and the rostral trunk may course well above the nerve. If the artery bifurcates distal to the nerve, only the main trunk will be involved in the compression. The point of bifurcation of the SCA affects the caliber of the vessel that makes contact with CN V; the contacting vessel will be of a smaller caliber if the SCA bifurcates before reaching CN V.
A less common source of compression of CN V is by the AICA. The AICA may have a high origin and loop upward to indent the medial or lower surface of CN V prior to passing downward to course with CNs VII and VIII (Figs. 2.5f and 2.6f). A serpentine basilar artery may also wander laterally and compress the medial side of CN V (Fig. 2.6g) (Apfelbaum 2000; Barker et al. 1996; Lorenzoni et al. 2008; Sunderland 1948; Thomas and Vilensky 2014). This type of basilar artery is often elongated and has a fusiform configuration. More than one artery may compress the nerve, for example, in some cases the SCA compresses the rostral surface of the nerve and the AICA compresses the caudal surface. Infrequently, a tortuous and arteriosclerotic vertebral artery or an upward loop of the PICA may reach and groove the undersurface of CN V. In the latter cases, CN XII may be stretched and thinned by the tortuous artery, and care should be taken to avoid damaging CN XII during the arterial mobilization. CN VI, located medial to the vertebral artery, should also be kept in mind during mobilization from lateral to medial, even though the nerve is difficult to expose sufficiently. CN V may also be compressed by a large pontine branch of the basilar artery, which passes around and penetrates the pons (Figs. 2.5e and 2.6e) (Rhoton 2000b).
Although rarer than arterial compression, compression and distortion of CN V by the surrounding veins also is found in trigeminal neuralgia (Figs. 2.7 and 2.8) (Hong et al. 2011; Matsushima et al. 2004). The superior petrosal veins and their tributaries are the most frequent veins compressing CN V. The transverse pontine veins, which pass transversely near CN V, are the most frequent veins to compress CN V. They may course medially in the axilla of the nerve or pass above, below, or lateral to the nerve and may indent any of its surfaces. The vein of the middle cerebellar peduncle may compress the lateral or medial surface of CN V before joining the superior petrosal veins emptying into the superior petrosal sinus. The vein of the cerebellopontine fissure may indent the lateral margin of CN V as it ascends toward the superior petrosal sinus, and the pontotrigeminal vein may indent the upper margin of the nerve. The junction of these veins, which converge and form a single trunk prior to entering the superior petrosal sinus, is usually lateral to CN V (Matsushima et al. 1983, 2014). This junction, however, may be located medial to CN V, in which case the common trunk must pass around CN V prior to reaching the superior petrosal sinus. These common venous trunks also may compress CN V.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
