A solid mass on the tympanic membrane

Significance statement

This is an extremely rare case of schwannoma as a tympanic membrane mass without extending to middle ear or occluding the external ear canal in an adult female. This case highlights the importance of approaching tympanic membrane lesions cautiously by endoscopic ear surgery, given the differential diagnosis for a solid tumor in this location.

We reported a 24-year-old woman presented with a sensation of aural fullness over right ear for two months. Otoscopic examination showed a bump riding on the anterior-inferior part of the tympanic membrane (Figure 1A). Pure tone audiogram showed normal hearing range but a 10 dB air-bone conduction gap in right-sided 2 K Hz. Tympanometry test was normal. High-resolution computed tomography (HRCT) of temporal bone showed a small lesion (size: 3.5 mm) attaching the outer border of right tympanic membrane (Figures 1C and 1D). The patient was performed with a transcanal endoscopic surgery under general anesthesia. The lesion was dissected from the fibrous layer of eardrum totally without perforation (Figures 1B and 2A). The specimen was totally embedded and the pathological finding showed spindle cells arranging in intersecting fascicles with nuclear palisading (Figures 2C and 2D) and positive S-100 protein immunochemical staining (Figure 2E), which are consistent with the diagnosis of schwannoma. Post-operative healing of tympanic membrane was uneventfully within 2 weeks (Figure 2B). Normal hearing without air-bone gap was examined and no recurrence of the tumor during 2-year follow-up.

Figure 1.

(A) Otoscopic image showed a dome-shaped lesion in anterior-inferior part of the eardrum. (B) The eardrum was intact without perforation after removal of the lesion immediately. (C) Axial and (D) coronal view of HRCT of temporal bone showed a small lesion in size of 3.5 mm attaching the outer border of right tympanic membrane.

Figure 2.

(A) The specimen was soft and yellowish. (B) The eardrum showed spontaneous healing 2 week after surgery. (C) The specimen (original magnification X40) was totally embedded. (D) Hematoxylin and eosin stain (original magnification X200) revealed cellular short spindle tumor cells proliferation in fascicular pattern and (E) diffusely S100 reactivity (original magnification X400).

Schwannoma are slow-growing benign tumors but arising from tympanic membrane is extremely rare.^1,2 Differential diagnosis of this tumor includes lipoma, hemangioma, fibroma, paraganglioma, and malignancy.^1-8 The patients usually presented with conductive hearing loss and different otologic symptoms according to the size and extent of tumors. HRCT of the temporal bone is crucial for evaluation of the extension of the tumor. However, it is difficult to confirm the origin of tumor when the tumor initially has extended to middle ear cavity or external ear. In general, the tumor was finally recorded where it arose during the operation. We demonstrated the first case of schwannoma only localized within the tympanic membrane without extending to middle ear or occluding the external ear canal.^1,2

The treatment of tumor arising from the tympanic membrane is surgical intervention using microscopy or endoscopy through the transcanal or endaural approach. During the surgery, the eardrum might be possible to be perforated which necessitates immediate tympanoplasty. ³ In our presented case, the lesion was dissected smoothly from the fibrous layer of eardrum without perforation by endoscopic ear surgery.

Primary masses of the tympanic membrane are rare and should be surgically explored to definitively establish pathology. ⁶ Although primary tympanic membrane masses almost are benign, few cases of malignancy have been reported to pursue the biopsy before complete excision.^5,8 This case highlights the importance of approaching tympanic membrane lesions cautiously, given the broad differential diagnosis for a solid tumor in this location.