Sites of arterial compression of the trigeminal nerve
A. Compressed by a tortuous basilar artery and the left trigeminal nerve is compressed by the main trunk of the SCA.
B. SCA bifurcates into rostral and caudal trunks before reaching the trigeminal nerve. The nerve is compressed by the caudal trunk.
C. SCA bifurcates distally to the nerve. The nerve is compressed by the main trunk.
D. SCA bifurcates before 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. The SCA passes around the brainstem above the nerve.
- The site of the skin incision (solid line) and the craniotomy (interrupted line) are shown in the insert.
- The superolateral margin of the cerebellum is gently retracted to expose the trigeminal nerve and the SCA.
- The brain spatula is advanced parallel to the superior petrosal sinus.
- The trochlear nerve is at the superior margin of the exposure and the facial and vestibulocochlear nerves are at the lower margin.
A. The trigeminal nerve 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.
G. Compression by a tortuous basilar artery
- SCA loops downward and, at the junction of the rostral and caudal trunks, contacts the posterior trigeminal root at the pontine junction.
- The cerebellar lip projects forward and may block access to the junction of the trigeminal nerve and pons in the retrosigmoid approach
- Early SCA bifurcation.
- The rostral trunk loops downward and indents the upper surface of the trigeminal nerve
- Later SCA bifurcation: another SCA passes around the pons and bifurcates into its rostral and caudal trunks above the trigeminal root entry zone.
Sites of venous compression of the trigeminal nerve
- A. The veins that commonly compress the trigeminal nerve are tributaries of the superior petrosal vein.
- Transverse pontine veins
- Course transversely across the pons
- Pontotrigeminal veins
- Arises on the upper pons and passes above the trigeminal nerve.
- Veins of the cerebellopontine fissure
- Arises along the cleft between the pons and the cerebellum
- Ascends behind the trigeminal nerve.
- Veins of the middle cerebellar peduncle.
- Rises in the region of the facial and vestibulocochlear nerves and ascends on the pons.
- 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.
Cer., cerebellar; Cer. Pon., cerebellopontine; Fiss., fissure; Mid., middle; Ped., peduncle; Pon., pontine; Sup., superior; Trans., transverse; Trig., trigeminal; V., vein
- The insert shows the site of the scalp incision (solid line) and the craniotomy (interrupted line).
- The cerebellum has been elevated to expose the junction of the trigeminal nerve with the pons. The superior petrosal veins empty into the superior petrosal sinus. The trochlear nerve is at the superior margin and the facial and vestibulocochlear nerves are at the lower margin of the exposure. The craniotomy exposes the junction of the sigmoid and transverse sinuses.
- A. The trigeminal nerve 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. The trigeminal nerve 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
Cer., cerebellar; Cer. Pon., cerebellopontine; Fiss., fissure; Mid., middle; Ped., peduncle; Pon., pontine; Sig., sigmoid; Sup., superior; Trans., transverse; Trig., trigeminal; V., vein
Neurovascular relationships of an acoustic neuroma
Anterolateral view
- The tumor arises from the vestibulocochlear nerve
- Tumour displaces
- Facial nerve anteriorly,
- Trigeminal nerve superiorly
- Vagus and glossopharyngeal nerves inferiorly.
- The facial nerve, even though displaced by the tumor, enters the brainstem along the lateral margin of the pontomedullary sulcus, rostral to the glossopharyngeal and vagus nerves, anterior to the flocculus, and rostral to the choroid plexus protruding from the foramen of Luschka.
- The rostral trunk of the AICA, after passing below the tumor, returns to the surface of the middle cerebellar peduncle above the flocculus.
- The veins displaced around the medial side of the tumor are the
- Veins of the middle cerebellar peduncle,
- Veins of the cerebellomedullary fissure,
- Veins of the cerebellopontine fissure,
- Veins of the pontomedullary sulcus,
- Retro-olivary Veins
- Lateral medullary veins.
Anterosuperior view
- The tumor arises from the vestibulocochlear nerve and displaces the facial nerve anteriorly, the trigeminal nerve superiorly, and the glossopharyngeal and vagus nerves inferiorly.
- The vestibulocochlear nerve disappears into the tumor.
- The facial nerve enters the brainstem along the lateral margin of the pontomedullary sulcus, rostral to the glossopharyngeal nerve, anterior to the flocculus, and rostral to the choroid plexus protruding from the foramen of Luschka.
- The AICA is usually displaced around the lower margin of the tumor.
- The veins displaced around the medial side of the tumor are the veins of the pontomedullary sulcus, middle cerebellar peduncle, and cerebellomedullary fissure, and the lateral medullary and retro-olivary veins.
Posterior inferior view via a suboccipital craniotomy
- The facial nerve is displaced anteriorly and superiorly in the cerebellopontine angle and enters the brainstem at the lateral end of the pontomedullary sulcus, anterosuperior to the choroid plexus protruding from the foramen of Luschka, and near where the flocculus is attached along the margin of the lateral recess.
- The tumor displaces the trigeminal nerve upward and the glossopharyngeal and vagus nerves downward.
- The AICA gives rise to a subarcuate artery, which enters the subarcuate fossa in the posterior wall of the internal acoustic meatus and bifurcates into a rostral and a caudal trunk.
- The rostral trunk courses above the flocculus to reach the surface of the middle cerebellar peduncle.
Posterior views via retrosigmoid approach
- Ch. Pl., choroid plexus; Co., cochlear; I.A.A., internal auditory (labyrinthine) artery; I.V., inferior vestibular; Mea., meatal; P.I.C.A., posteroinferior cerebellar artery; Post., posterior; R.P.A., recurrent perforating artery; S.A., subarcuate artery; S.V., superior vestibular; S.C.A., superior cerebellar artery; Seg., segment; Tent., tentorium
- Top left, the insert shows the direction of view.
- Both the premeatal and the postmeatal segments are in their most common locations around the lower margin of the tumor.
- Premeatal segment approaches the meatus from anteroinferior
- Postmeatal segment passes posteroinferior to the tumor.
- The SCA and the trigeminal nerve are above the tumor, and the PICA and the glossopharyngeal, vagus, and spinal accessory nerves are below the tumor.
- The choroid plexus protrudes into the cerebellopontine angle medial to the tumor.
- The posterior wall of the internal acoustic canal has been removed to expose the transverse crest and the superior vestibular and inferior vestibular nerves.
- The vestibular nerves disappear into the tumor;
- However, the cochlear and facial nerves are displaced around the anterior margin of the tumor.
- A subarcuate artery arises from the premeatal segment, and a recurrent perforating artery arises from the postmeatal segment.
- Center right
- In a less common pattern of displacement of the AICA, the premeatal and postmeatal segments are above the tumor.
- The internal auditory arteries arise from the meatal segment.
- Bottom left
- Both the premeatal and the postmeatal segments of AICA are displaced anteriorly to the tumor.
- This occurs if the AICA courses between the vestibulocochlear and facial nerves.
- The tumor arises in the vestibular nerves, and tumor growth displaces both the premeatal and the postmeatal segments anteriorly.
- The tumor arises from the vestibulocochlear nerve and displaces the facial nerve anteriorly, the trigeminal nerve superiorly, and the glossopharyngeal and vagus nerves inferiorly.
- The vestibulocochlear nerve disappears into the tumor.
- The facial nerve enters the brainstem at the lateral margin of the pontomedullary sulcus anterior to the flocculus and rostral to the choroid plexus protruding from the foramen of Luschka.
- The rostral trunk of the AICA courses below the tumor and above the flocculus to reach the surface of the middle cerebellar peduncle.
- The veins displaced around the medial side of the tumor are the lateral medullary veins and the veins of the middle cerebellar peduncle, cerebellomedullary fissure, and pontomedullary sulcus.
- The vein of the cerebellopontine fissure passes above the tumor.
- A recurrent perforating branch of the AICA passes across the tumor and supplies the brainstem.
Neurovascular relationships in hemifacial spasm
Abbreviations
- A., artery; A.I.C.A., anteroinferior cerebellar artery; Cer., cerebellar; Chor. Plex., choroid plexus; CN, cranial nerve; Flocc., flocculus; Inf., inferior; Intermed., intermedius; Labyrin., labyrinthine; Mea., meatal; Mid., middle; Nerv., nervus; Ped., peduncle; Pet., petrosal; P.I.C.A., posteroinferior cerebellar artery; Post., posterior; Seg., segment; Subarc., subarcuate; V., vein; Vert., vertebral.
Facial nerve exposure via retrosigmoid approach in hemifacial spasm
- A large tortuous PICA loops upward anterior to the facial and vestibulocochlear nerves and behind the trigeminal nerve, before turning downward to reach the medulla.
- The flocculus and the choroid plexus protruding from the foramen Luschka often hide the junction of the facial and vestibulocochlear nerves with brainstem.
- In this case, the flocculus has been gently elevated to expose the junction of these nerves with the brainstem.
- Exposing the facial nerve exit zone from the brainstem is facilitated by directing the exposure along the inferolateral margin of the cerebellum in the area above the glossopharyngeal nerve and below the lower edge of the flocculus.
- The vestibulocochlear nerve has been depressed.
- This exposes the distal segment of the facial nerve, but does not provide access to the junction of the facial nerve with the brainstem, which should be visualised in dealing with hemifacial spasm.
- The vestibulocochlear nerve has been gently elevated.
- This exposes both the rostral and caudal margins of the facial nerve at the brainstem.
- A rootlet of the nervus intermedius is also exposed.
- The vein of the middle cerebellar peduncle passes between the facial and vestibulocochlear nerve.
- The lower drawing shows the surgical exposure obtained with this approach.
- The AICA and the facial and vestibulocochlear nerves are in the midportion of the exposure.
- The vertebral artery, PICA, and the glossopharyngeal, vagus, and spinal accessory nerves are below.
- The cerebellum is elevated to expose the facial and vestibulocochlear nerves and the premeatal, meatal, and postmeatal segments of the AICA.
- The flocculus and the choroid plexus block the view of the junction of the facial and vestibulocochlear nerves with the brainstem.
- The flocculus and the choroid plexus have been elevated to expose the root entry/exit zone of the facial and vestibulocochlear nerves.
- The premeatal segment compresses the nerves at the junction with the pons and the medulla.
- The nerve root entry/ exit zone is compressed by the postmeatal segment.
- A tortuous PICA loops upward to compress the nerves at their junction with the brainstem before turning inferiorly to pass between the glossopharyngeal and vagus nerves.
- A tortuous vertebral artery compresses the nerve root entry/exit zone.
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