Ear, Nose & Throat Journal2024, Vol. 103(1) 13–18© The Author(s) 2021Article reuse guidelines:sagepub.com/journals-permissionsDOI: 10.1177/01455613211026397journals.sagepub.com/home/ear
AbstractGreater superficial petrosal nerve (GSPN) schwannomas are an exceedingly rare nerve sheath tumor. The current literature search was conducted using Medline and Embase database by key search terms. Only 31 cases have been reported in the literature so far. Facial palsy, hearing loss, and xerophthalmia accounted for 48.4% (15), 41.9% (13), and 29% (9) of all cases, respectively. The middle cranial fossa approach was used in all previous reports. A retrospective review of 2 GSPN schwannomas patients treated by endoscopic endonasal approach (EEA) in our center was collected. Clinical records, including clinical features, pre- and postoperative images, surgery, and follow-up information, were reviewed. In all cases, clinical features including facial numbness and headache were found, with tinnitus in case 1, hearing loss, xerophthalmia in case 2. Imaging studies showed a solid mass that originated in the anterior of the petrous bone. Two patients were treated by EEA. Furthermore, no recurrence was found during the follow-up period (15-29 months) in both of the 2 cases after the operation. Complete resection of GSPN schwannomas can be achieved via the pure EEA. Endoscopic endonasal approach for radical removal of tumors is safe and feasible.
Keywordsgreater superficial petrosal nerve, schwannomas, endoscopic endonasal
Greater superficial petrosal nerve (GSPN) schwannoma is a very rare type of facial nerve schwannoma, and few cases have been reported in literature. Common symptoms of GSPN schwannoma include facial palsy, hearing loss, headache, and xerophthalmia.1,2 Imaging studies showed a solid mass that originated in the anterior of the petrous bone. Although middle cranial fossa approach was used in all previous reports1-19 in GSPN schwannoma removal, the diagnostic criteria and optimal surgical strategies are still lacking. Here, we present 2 cases of schwannoma occurring in GSPN treated via pure endoscopic endonasal approach (EEA) and give a review of previously reported cases.
A 39-year-old woman complained of left-sided tinnitus and dizziness for one month and headache for 2 weeks. Four years ago, this patient was diagnosed with “schwannoma in left parotid and pterygopalatine fossa” because of intermittent left ear pain, pulsatile tinnitus, and cheek numbness. A subsequent surgery led to postoperative left facial paralysis that has not been alleviated since then. Neurologic examination showed left-sided facial paralysis (grade 4 according to the House-Brackmann classification). The preoperative magnetic resonance imaging (MRI) demonstrated an inhomogeneous mass (3.7 cm × 2.6 cm × 3.3 cm) with an enhanced signal intensity located at the left pterygopalatine fossa and petrous bone, with extension into the left cavernous sinus (Figure 1A and B). Gross total removal was achieved using a pure EEA. The surgical procedure took about 2 hours; intraoperative bleeding was 400 mL. The patient was discharged 9 days after surgery. Eight days after surgery, the MRI image showed that the tumor had been removed completely. Histopathological examination revealed that the lesion was schwannoma. At the 15-month follow-up, there was no evidence of recurrence (Figure 1C and D).
A 64-year-old woman presented with left-sided hearing loss for 8 years and facial numbness for 6 months. The patient was diagnosed with left-sided hearing loss, ear fullness accompanied by intermittent headache and dizziness 8 years ago. The symptoms aggravated gradually over the years. It was decreasing in tear secretion of the left eye, as supported by Schirmer’s test. An admission hearing examination revealed left-sided mixed type deafness, and left ear tympanometry showed curves type “B.” Computed tomography (CT) and MRI demonstrated an enhancing solid mass measuring 2.1 × 1.8 cm in the left middle cranial fossa, over the superior edge of the petrous bone with extension to the internal auditory canal (Figure 2A and B; Figure 3A and B). Gross total removal was achieved using a pure EEA. The entire surgical procedure took 3 hours; intraoperative bleeding was 500 mL. The patient was discharged 12 days after surgery. The MRI performed 12 days after surgery showed that the tumor had been removed completely. Histopathological examination revealed that the lesion was schwannoma. At the 29-month follow-up, there was no evidence of recurrence (Figure 3C and D).
A total of 31 patients with GSPN schwannomas were identified. The average age of the patients is 40 years, and the ratio of women to men was 17:14. The symptoms of GSPN schwannoma include facial palsy, hearing loss, headache, xerophthalmia, tinnitus, vertigo, eye pain, and possibly diplopia. Facial palsy, hearing loss, and xerophthalmia accounted for 48.4% (15), 41.9% (13), and 29% (9) of all cases, respectively. All patients were treated with the middle cranial fossa approach. Ten patients were treated with extradural and intradural subtemporal approaches. Nineteen patients were treated with the extradural middle fossa approach. Eleven patients had partial improvement in preoperative symptoms. There were 11 patients who had no xerophthalmia before surgery but developed this symptom after surgery. Patients with xerophthalmia did not improve after surgery.
Facial nerve schwannoma is an uncommon nerve sheath tumor and comprising around 0.8% of all intrapetrous mass lesions. The schwannomas may arise from tympanic, vertical, labyrinthine, geniculate, and meatal segment of the facial nerve in petrous bone, and in some cases even extend to middle cranial fossa.1 Schwannoma involving GSPN, a branch of the facial nerve, is a very rare subtype of facial nerve schwannoma.
Greater superficial petrosal nerve, which derived from the geniculate ganglion, innervates the lacrimal gland and the mucous membrane of the nasal cavity and the palate. Greater superficial petrosal nerve goes forward through the hiatus of the facial canal located on the anterosuperior aspect of the petrous bone to join the deep petrosal nerve, forming the Vidian nerve.2 Greater superficial petrosal nerve schwannoma may arise anywhere along the course of the facial nerve. In the middle fossa, the GSPN was extradual and closed to the petrous segment of the internal carotid artery (ICA). It is very important to identify the delicate anatomy of the nerves and vascular in the region of petrous apex before surgery.6
Only 31 GSPN schwannoma cases have been reported from 1936 to 2019 (Table 1).1-19 The average age of the patients is 40 years, and most cases are females in previous reports. Common symptoms of GSPN schwannoma include facial palsy, hearing loss, headache, xerophthalmia, and possibly diplopia.1,2 Although xerophthalmia is considered pathognomonic for GSPN, it may not happen in all patients and only present if parasympathetic nerve fibers have been destroyed by the tumor.2,3 We cannot exclude the possibility of GSPN only by lacrimation. Other symptoms that need to be considered include headache, eye pain, and trigeminal nerve affection.4 It is difficult to estimate whether a tumor arises from the GSPN relies on these symptoms. Nevertheless, for the preoperative clinical testing of GSPN, measurement of bilateral tear secretion is still recommended.5
Greater superficial petrosal nerve schwannoma is an epidural lesion that originate at the middle cranial fossa and extend from the facial hiatus to the foramen lacerum.2,4-7 The typical CT imaging of GSPN schwannoma shows benignappearing bony scallop and remodeling of the bony boundaries in the anteromedial aspect of the petrous bone.5,8 Computed tomography is also helpful to reveal the relationship between the lesion and bone destruction of the carotid canal. Magnetic resonance imaging can be applied to reveal the locations of the tumor. Magnetic resonance imaging shows tumor iso- to hypointense relative to gray matter on T1-weighted image and heterogeneously hyperintense on T2-weighted image.1 Contrast-enhanced MRI presents a heterogeneously enhanced mass in the middle cranial fossa. Histologic examination reveals a typical biphasic schwannoma containing Antoni A and B tissue types. Trigeminal nerve schwannoma, facial nerve schwannoma, and meningioma of the middle cranial fossa can be differentiated and diagnosed by their images’ characteristics in most cases.7,9 Schwannoma originating from geniculate ganglion usually has a “bulbous” enlargement at the geniculate fossa.5,10 The origin of most meningioma tends to be at the dura and grow intradurally into the arachnoid space.7 Trigeminal schwannoma arises from the petrous apex around Gasserian ganglion and Meckel’s cave. Both our patients feel facial numbness, but their images showed the tumor did not extend to the foramen rotundum and ovale. Although the lesion damage petrous bone, no apparent damage to facial nerve bone canal was observed. Tumor that originate from the facial hiatus to the foramen lacerum could be GSPN schwannoma. The preoperative diagnoses of GSPN schwannoma should combine the radiological characteristics and histologic examination. The final pathological diagnosis confirmed schwannoma, but it does not provide the lesion site. Presently, MRI is the only method to identify schwannoma originate from GSPN. In our study, preoperative MRI demonstrated that tumor adjoined to ICA in case 1 and extended to cavernous sinus and circumvented ICA in case 2. The relationship between the mass and the carotid canal should be assessed in case of the occurrence of serious complications. If the ICA is involved, angiography and a preoperative occlusion examination are recommended.7
Greater superficial petrosal nerve schwannomas are in the extradural space of the middle fossa. The extradural middle fossa approach was used in previous reports with total removal and low postoperative complication.2-5,7,11,12 However, the intradural approach would be preferred to prevent injury to the ICA and the geniculate ganglion compared with the extradural approach.13 Parameters including tumor size and main symptoms help doctors decide whether intra or extradural subtemporal approach should be taken.6 We have accomplished many dissections for EEA, from nose to petrous apex. We also have experience in treating lesion on the petrous apex. This is the first time to report 2 cases of GSPN schwannoma that underwent surgery via the pure EEA. Two patients in our study did not show recurrence after surgery. Headache and tinnitus in case 1 have improved, and facial numbness and headache in case 2 have improved. Xerophthalmia is a common surgical complication after surgery. Meningitis, cerebrospinal fluid leak, and other serious complications did not occur. From our experience, EEA for GSPN schwannoma is suitable for treatment lesion located in the medial of petrous bone without affecting the mastoid. Surgeons’ experience also plays a crucial role. We have successively exposed maxillary sinus, pterygopalatine fossa, and petrous apex during surgery, followed by intracapsular removal of the tumor and protected cranial nerve V2-3 and ICA. Compared with middle fossa approaches, the advantages of the EEA including visualization of the tumor and its adjacent structures, improvement or preservation of cranial nerve function, and decreased tissue trauma and without external incision (Figure 4A-F). Therefore, EEA for total removing GSPN schwannoma is feasible and safe.
Greater superficial petrosal nerve schwannoma is an extremely rare type of facial nerve tumor and can be completely and safely removed by EEA. Preoperative diagnosis based on clinical features together with CT and contrast MRI facilitate the reveal of tumor location in differential diagnosis. Early diagnosis and surgical intervention will help to preserve facial nerve functions. In the past, surgeons have more experience for GSPN schwannoma excision by middle cranial fossa approach. Our results show that the EEA can also be selected for complete removal of GSPN schwannoma and without serious complications in patients. Otolaryngology and neurosurgery doctors should evaluate the symptoms and lesion images together to determine the most appropriate surgical management.
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Siyuan Zhang https://orcid.org/0000-0002-9422-8772
1 Department of Otorhinolaryngology Head and Neck Surgery, Xuanwu Hospital, Capital Medical University, Beijing, China
2 Department of Neurosurgery, Skull Base Surgery Center, Xuanwu Hospital, Capital Medical University, Beijing, China
Received: December 07, 2020; revised: May 16, 2021; accepted: June 01, 2021
Corresponding Author:Zhenlin Wang, MD, Department of Otorhinolaryngology Head and Neck Surgery, Xuanwu Hospital Capital Medical University, No. 45 Changchun Street, Xicheng District, Beijing 100053, China.Email: wzl1812@xwhosp.org
