Features and management of a schwannoma of the chorda tympani and review of the literature

Abstract

Intrinsic facial nerve tumors are rare lesions. Among the different histology types, schwannomas is the most frequently reported in literature. Other histological types of facial nerve tumors are hemangiomas, meningiomas, and neurofibromas. Chorda tympani schwannomas (CTSs) are extremely rare entities and are considered as an independent subgroup of facial nerve schwannomas because of their clinical characteristics. The aim of this report is to present the clinical and radiological features and the management of a CTS in a 27-year-old male presenting with conductive hearing loss.

Background

Intrinsic facial nerve tumors are rare lesions. Among the different histology types, schwannomas are the most frequent.

Other histological types of facial nerve tumors are hemangiomas, meningiomas, and neurofibromas. Chorda tympani schwannomas (CTSs) are extremely rare entities and are considered as an independent subgroup of facial nerve schwannomas because of their clinical characteristics.

The aim of this report is to present the clinical and radiological features and the management of a CTS in a 27-year-old male presenting with conductive hearing loss.

A review of the literature is also reported.

Case report

A 27-year-old male presented to ENT department with a 4-months history of left hearing loss. He denied tinnitus, vertigo, facial palsy, and dysgeusia. Otoscopic examination revealed an intact but lateralized tympanic membrane and a retrotympanic pink mass. First, a tympanic paraganglioma was suspected even if the patient presented a non-pulsatile mass and the color was not the characteristic reddish blue.

Audiometric tests revealed a left to mild conductive hearing loss, stapedial reflexes were absent, and tympanometry was type B.

A CT scan was performed revealing an isodense-to-soft-tissue mass occupying most of the tympanic cavity without signs of bone and/or ossicular erosion. Mastoid was well-aerated. Petrous bone MRI with gadolinium was therefore indicated. It showed the presence of a 10 × 6 × 13 mm mass lying on the cochlear promontory, isointense to the brain parenchyma on T1-wi, inhomogeneously hyperintense on T2-wi, and with intense enhancement after gadolinium administration. The neuroradiologist corroborated the clinical diagnosis of tympanic paraganglioma.

Microscopic post-auricular tympanoplasty was then performed. After elevation of tympanomeatal flap, the tympanic cavity was almost totally occupied by a yellow-white mass extending from the tympanic tube orifice to the anterior and posterior epitympanum, mesotympanum, and retrotympanum (Figure 1). A careful analysis of the tympanic cavity revealed a mass originating from chorda tympani (CT) (Figure 2); therefore, a n intraoperative suspicion of schwannoma of the CT was postulated. In consideration of the mass extension, surrounding the ossicular chain, a mastoidectomy was performed to control adequately its extension to the posterior epitympanum and antrum. The head of the malleus and the incus were removed to ensure a complete excision of the mass and to avoid sensorineural hearing loss during surgical maneuvers. At the end of surgery, partial ossiculoplasty was performed using autologous remodeled incus (IRA) between the handle of the malleus and the capitulum of the stapes. Lastly the tympanic membrane was repositioned.

Figure 1.

Intraoperative finding of the tympanic cavity after elevation of the tympanomeatal flap through a microscopic transcanal retroauricolar view. m, malleus; pml, posterior malleolar ligament; p, promontory; cts, chorda tympani schwannoma.

Figure 2.

Intrapoperative view of the mass originating from CT. m, malleus; cts, chorda tympani schwannoma; ct, chorda tympani; s, stapes.

Histologic examination confirmed the intraoperative suspicion of chorda tympani schwannoma.

The patient was followed up at 1 month, 3 months, 6 months, and 12 months. At the last follow-up, the patient was in good health, with an intact tympanic membrane and without recurrence at CT scan. Audiometry revealed a closure of the air-bone gap.

Discussion

The CT is the second branch of facial nerve (FN). It arises from the mastoid tract (third tract) of the FN, just before that the FN emerges from the stylomastoid foramen. At the level of the chordal eminence of the retrotympanum, the CT becomes intratympanic passing between the long process of the incus and the handle of the malleus. It exits anteriorly through the anterior (or medial) canalicus (also called Huguier or Civinini canal) which is one of the two canals of the petrotympanic fissure. The lateral canal is larger and permits the passage of the anterior tympanic artery, also named Glaserian artery, a branch of the internal maxillary artery, and the anterior ligament of malleus. After leaving the temporal bone, CT descends in the infratemporal fossa joining the lingual nerve. It provides gustatory sensation to the anterior two-thirds of the tongue and carries parasympathetic fibers to the submandibular and sublingual salivary glands.^1,2

Schwannomas of the CT are very uncommon tumors. From our knowledge, this is the 21st case of CTS since the first was published by Nager in 1969, where a case of CTS in a patient with neurofibromatosis 1 was presented. ³

Table 1 summarizes all the cases of CTS present in the English literature.

Table 1.

Literature review of patients affected by chorda tympani schwannoma.

Authors	Age/sex	Side	Clinical presentation	Otoscopic examination	Imaging examination	Surgery	Postoperative clinical evaluation
Lu et al 4	31/F	Left	Tinnitus, conductive HL	Mass in the upper part of tympanic cavity and thickened TM	Soft tissue mass of the left middle ear tympanum	Endoscopic transcanal approach/TORP	Normal
Furukawa et al 5	37/M	NR	HL	NR	NR	Endoscopic transcanal approach	Temporary taste disturbance; no recurrence
	59/M	Right	Mixed HL	Light red mass occupying the posterior middle year	Soft tissue mass from behind the ossicles to the retrotympanum and ossicular chain erosion	Endoscopic transcanal approach/IRA	Temporary taste disturbance; no recurrence
Schwam et al 6	59/M	Right	Tinnitus and episodic vertigo	Retroympanic mass	Tympanic nodular lesion abutting the scutum and cochlear promontory, inseparable from TM	Endoscopic transcanal approach, no ossicular chain disrupment	Normal
Montava et al 7	89/M	Right	Asymptomatic in patient with MOE	Otorrhea and inflammation, thickened TM	Opacification of middle ear cavity, osteolytic erosion along the vertical segment of the VII cn	Biopsy	No surgery
Undabeitia et al 8	45/M	Right	Mixed HL, vertigo	Greyish mass in the posterior tympanic areas	Mass in the right tympanic box	Retroauricolar Tm approach, PORP with tragal cartilage	FP HBII, mixed HL
Huoh and Cheung 9	24/F	Right	HL, tinnitus, FP present early in child- hood in NF type 2	Retrotympanic mass	Chorda tympani tumor	No surgery	No surgery
Hopkins et al 10	53/M	Right	Vertigo, mixed HL	Soft tissue mass in the postero-superior quadrant	Soft tissue mass in the postero-superior quadrant of the middle ear extending into the attic	Retroauricolar Tm approach, no ossicular chain disrupment	Temporary taste disturbance
Biggs and Fagan 11	26/F	Right	Earache, otorrhea	Retrotympanic mass	Tumors in the hypotympanum	Retroarticular Tm approach, no ossicular chain disrupment	Normal
Magliulo et al 12	58/F	Left	Conductive HL, tinnitus	Mass in the EAC	Mass in the EAC extending in the lower tympanic cavity, small osteolytic erosion along the vertical segment of the VII cn	Retroarticular Tm approach, ossiculoplasty	Normal
Chai et al 13	60/F	Left	Conductive HL	Mass adjacent to an intact TM	Lesion medial to the malleus extending into the attic	Retroauricolar approach, IRA	Normal
Browning et al 14	51/F	Right	Mixed HL, earache	Mass in the postero-superior EAC	Normal	Retroauricolar Tm approach, no ossiculoplasty	Normal
Saleh et al 15	62/F	Left	Tinnitus	Mass in the postero-superior EAC	NR	Retroauricolar Tm approach	Normal
Lopes Filho et al 16	25/M	Right	Fullness, earache	Mass in the posterior EAC	Normal	Retroauricolar approach, Tm	Normal
Sanna et al 17	14/F	Right	Progressive FP	NR	Normal	Retroauricolar TM approach	FP HB II
Wiet et al 18	12/M	Left	Conductive HL	Mass in the EAC	Mass in the EAC and erosive changes of the posterior wall	Argon laser, retroauricolar approach	NR
	55/M	Left	Conductive HL, tinnitus	Anterior tympanic mass	NR	Retroauricolar approach	Normal
Babin et al 19	18/M	NR	Asymptomatic in MP type V	NR	NR	NR	Post-Mortem study
Pou and Chambers 20	18/F	Right	Conductive HL, tinnitus	Mass in the EAC	Small mass in the EAC	Tm approach/IRA	Normal, no recurrence
Nager 3	22/M	NR	NR, NF type 1	NR	NR	NR	NR

M, Male; F, Female; NR, Not Reported; HL, Hearing Loss; FP, Facial Palsy; EAC, External Auditory Canal; HB, House-Brackmann Grade; MP Mucopolisaccarydoses; NF, Neurofibromatosis; NR, Not Reported; TM, Tympanic Membrane; VS, Vestibular Schwannoma; MOE, Malignant Otitis Externa; Tm Transmastoyd; IRA, Autologous Remodelled Incus.

Among the 21 patients, a male predominance emerged: 12 were male and 9 were female. The mean age at diagnosis was 37.9 years (range 12–89 years). Tumor was on the left side in 7 cases and on the right in 11 cases. Side was not specified in 3 out of 21 cases. Because there are no symptoms that uniquely typify CTS, this pathology is often misdiagnosed. Most reported symptoms are conductive or mixed hearing loss in 70% and tinnitus in 33.3% of the cases. Less reported symptoms were vertigos and earache in 14% of the cases, facial palsy in 2 out of 21 cases (9.5%), and otorrhea in 1 out of 21 cases (4.8%). In the reported case the patient complained a 4-month history of hearing loss without facial palsy or dysgeusia. Taste disturbance, indeed, has never been reported in any previous case; this is possibly due to the slow growth of the tumor. ⁷ In most cases (13 out of 21), CT scan revealed an isodense-to-soft-tissue mass of the middle ear, sometimes extended to the external auditory canal. In this case, the tumor occupied most of the tympanic cavity without signs of bone and/or ossicular erosion. After obtaining the histopathological diagnosis of CTS, we reviewed the CT scan images and noticed an enlargement of the petrotympanic fissure in sagittal view. As already described in the study of Sato et al., ²¹ the exit tunnel of petrotympanic fissure at tympanic cavity measured in sagittal views has an average exit diameter of 0.9 ± 0.4; in the reported case it was 1.905 mm (Figure 3). This sign has never been reported in the literature but, if present, it could be used as a radiological sign of CTS.

Figure 3.

Sagittal sections of CT scan (a) and MRI T1-wi with gadolinium (b) at the level of the petrotynoanic fissure.

The differential diagnosis includes paraganglioma, congenital or acquired cholesteatoma, hemangioma, adenoma, and meningioma. In all cases of middle ear neoplasms with an intact tympanic membrane, CT scan and MRI are required for an efficient preoperative work-up.^8,10,12,14 The greater value of MRI is to rule out cholesteatoma through the ADC sequences: cholesteatomas appear hyperintense on DWI but with a low signal area in ADC map while non-cholesteatomatous lesions do not. ²²

Furthermore, T1-wi after gadolinium administration showed hyperintensity of the facial nerve both at the level of the geniculate ganglion, the intralabyrinthine tract and the fundus of the internal auditory canal. This finding, revealed after a careful review of the imaging, represents a sign of irritation of the facial nerve, in particular the sensitive component (Wrisberg’s nerve), which is the reason why the patient did not manifest any motor symptoms (Figure 4). Moreover, the lack of both local and systemic inflammatory symptoms can lead to the suspicion of neoplastic etiology.

Figure 4.

MRI T1-wi with gadolinium showing the contrast enhancement of the facial nerve along its course. Fundus of the internal auditory canal (red arrow). Intralabyrinthine tract (green arrow). Geniculate ganglion (yellow arrow).

In recent years, transcanal endoscopic management of CTS, in addition to traditional microscopic, have been described.

Among the cases described in the English literature, including the one reported in this study, 13 patients underwent retroauricolar approaches and 5 patients underwent endoscopic transcanal approach. Two patients out of 21 did not have surgical resection and in 2 cases out of 21 the surgical approach was not specified.

In author’s opinion, the surgical approach should be chosen according to the extent of the disease and the surgeon’s experience: if the lesion affects the mastoid tract of CT or if extends to the antrum, a transmastoid retroauricolar approach is indicated.

In cases of extensive epitympanic involvement and ossicular chain embracement, the incus and the head of the malleus must be removed to avoid neurosensory damage during surgical maneuvers. The reconstructive choice should be oriented according to the case with autologous or artificial material. In the reported case, an ossiculoplasty with a remodeled autologous incus between the handle of the malleus and the capitulum of the stapes have been performed.

Final diagnosis is achieved by biopsy and differential histological diagnosis includes several other benign nerve sheath tumors, low grade MPNST (malignant peripheral nerve sheath tumor), and meningiomas.

Conclusion

Chorda tympani schwannomas is a very uncommon finding. Differential diagnosis includes several neoplasms that could originate primarily from the middle ear cavity such as tympanic glomus and congenital cholesteatoma. There are not distinctive symptoms, the most common is hearing loss. CT scan and MRI are both necessary for proper evaluation: CTS appears like an intratympanic mass, with or without extension in the external auditory canal or in the mastoid. The intense post-contrast enhancement in MRI, similar to tympanic glomus, could lead into error. The lack of bone erosion and the scalloping features of CTS in CT scan may help to make the right suspicion. Measuring the petrotympanic fissure on sagittal views of CT should be considered. Indeed, its enlargement could be used as a radiological sign of CTS. Moreover, hyperintensity in T1 with contrast should be evaluated.

However histological diagnosis is always necessary to confirm the nature of the lesion. Endoscopic or microscopic surgery strategies are both feasible with low morbidities even in cases of ossicular chain involvement.

ORCID iD

Francesco Maccarrone https://orcid.org/0000-0003-0508-519X