34 Large Trigeminal Neurinoma

ATUL GOEL AND KETAN I. DESAI

Diagnosis Large trigeminal neurinoma

Problem and Tactics A 20-year-old man with a large, dumbbell-shaped trigeminal neurinoma presented with an unusual symptom of pathological laughter. The tumor was radically resected by a lateral basal subtemporal approach. The patient was relieved of the pathological laughter immediately after the surgery.

Keywords Trigeminal neurinoma, subtemporal approach, pathological laughter, gasserian ganglion

Clinical Presentation

A 20-year-old male manifested uncontrollable explosive laughter during conversation over a 1-year period. The laughter lasted for a few seconds and stopped abruptly, after which the conversation would continue. During these periods he lost track of the conversation and was unaware of the pathological emotional outburst. The frequency of these episodes progressively increased over the 1-year period to four to five within half an hour of conversation. In addition he had paresthesiae and numbness in the right half of the face, giddiness, and progressively worsening ataxia for about the same period of one year.

Neurological examination showed that his higher functions were normal. Both fundi showed papilledema. The right corneal reaction was sluggish and there was hypesthesia in the maxillary and mandibular divisions of the trigeminal nerve. There were no other abnormal findings. Magnetic resonance imaging (MRI) showed a large tumor extending from the prepontine to the medial temporal region (Fig. 34–1A–E). The midbrain, pons, and cerebellum were severely deformed by the tumor. The petrous apex was eroded.

Surgical Technique

The patient was placed in a lateral position. Cranial nerve or brain stem function monitoring was not used. A continuous external drainage of cerebrospinal fluid by lumbar subarachnoid catheter placement was set up. The scalp incision is shown in Fig. 34–2A. It started from the point that was ~1.5 to 2 cm anterior to the tragus of the ear and ~1.5 cm inferior to the zygomatic arch. The incision was anterior to the trunk of the superficial temporal artery. Working deep to the deep layer of temporalis fascia and displacing the soft tissue harboring the frontal and zygomatic branches of the facial nerve anteriorly, protected by these tiny nerves. The incision initially curved superiorly and then traversed posteriorly. The incision exposed the squamous temporal and posterior parietooccipital bone, posterior third of the temporalis muscle, roots of the zygomatic arch, supramastoid crest, and base of the mastoid process. The wide base of the scalp flap and preservation of all feeding arteries ensured its adequate vascularity. The posterior aspect of the temporalis muscle was mobilized in the subperiosteal plane from the temporal bone and from the sharp superior border of the zygomatic arch. The muscle was then rotated anteriorly. A low temporal craniotomy with the base centered on the external ear canal was performed (Fig. 34–2B). The anterior and posterior roots of the zygomatic arch, the glenoid fossa, and the lateral half of the roof of the external ear canal were removed with the help of a power drill (Fig. 34–2C). The external ear canal was protected by sharp subperiosteal separation of the canal from the bony roof. The meniscus of the temporomandibular joint was exposed, but it was not removed. The superior third (~1.5–2 cm below and medial to the supramastoid crest) of the mastoid air cells was drilled. The mastoid antrum was not opened. The drilling of the mastoid process was continued medially to expose the bony labyrinth around the superior and posterior semicircular canals. The sigmoid sinus and the region of its junction with the transverse sinus were not exposed, and a thin plate of bone was left between the sinus and the mastoid exposure. The dura was now elevated off the middle fossa floor after sectioning the middle meningeal artery, and a basal extradural exposure was obtained as shown in Fig. 34–2C. An entirely extradural route can remove the tumors, which are limited to, or have a larger bulk in, the middle fossa, after exposing the foramen ovale and dissecting the outer sheath of the dura.¹

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