Greater petrosal nerve schwannomas—analysis of four cases and review of the literature

Abstract

Schwannomas arising from the greater petrosal nerve (GPN) are exceedingly rare: only 10 such cases have been reported in the English literature. We report on four cases of GPN schwannomas and discuss the surgical approach for their removal. Four patients with GPN schwannomas underwent surgery at Keio University Hospital. We present the pre- and postoperative clinical findings and describe the structures around the GPN schwannomas as observed during the surgery. Histological sections were performed around the GPN using Masson's trichrome stain to elucidate the membrane structures. Three patients presented with xerophthalmia, and one with facial palsy, hearing disturbance, and generalized convulsions. Contrast-enhanced magnetic resonance images revealed tumors in the temporal lobe. Bone-window computed tomography showed erosion of the anterior petrous apex. During the operation, the temporal lobe was retracted epidurally. The tumors were visible inside the interdural space and covered with the epineurium. In three cases, the tumors were completely removed, and in one case, the tumor was subtotally removed with intraoperative facial monitoring. In the histological sections, we confirmed that the GPN ran within the interdural space. Approaching epi- and interdurally is suitable for the removal of GPN schwannomas because the GPN is located within the interdural space. The advantage of this approach is that the landmark points can be identified. Moreover, the possibility of injuring the temporal lobe is low because the temporal lobe is not exposed in this approach.

Greater Superficial Petrosal Nerve Schwannoma: 3 Case Reports and Review of Literature

“…Facial nerve function usually improves following surgery, only in 3 of the previous reported cases it has either deteriorated or remained same as preoperative status [11,12]. All of our patients showed improvement in facial nerve function.…”

“…In previously reported cases only 6 patients had xerophthalmia [1,[12][13][14]. Other reported manifestations include diplopia due to abducens nerve palsy [1], trigeminal nerve involvement [15], seizure [12], eye pain, headache etc. One of our patient had xerophthalmia, all three had facial paresis.…”

“…Xerophthalmia, although pathognomonic of GSPN schwannoma may not be there in all patients and only present if parasympathetic nerve fibers have been destroyed by the tumor [7][8][9][10][11]. In previously reported cases only 6 patients had xerophthalmia [1,[12][13][14]. Other reported manifestations include diplopia due to abducens nerve palsy [1], trigeminal nerve involvement [15], seizure [12], eye pain, headache etc.…”

The Appropriate Surgical Approach to a Greater Petrosal Nerve Schwannoma in the Setting of Temporal Lobe Edema

“…[1][2][3] The labyrinthine, tympanic, and vertical segments are the most common sites. 4,5 Tumors originating in and restricted to the greater petrosal nerve (GPN) are the least frequent. The GPN dissociates at the geniculate ganglion (GG) of the facial nerve and runs anteromedially to exit the superior surface of the temporal bone via the GPN hiatus.…”

“…Xerophthalmia and facial nerve paralysis are the most common complications after surgery. 1,[5][6][7][8][9][10] We present a case of GPN schwannoma associated with temporal lobe edema in which the patient was operated on by an extradural and intradural middle fossa approach. To the best of our knowledge, GPN schwannomas associated with temporal lobe edema have not been reported previously.…”