Endolymphatic Sac Tumor Presenting as an External Ear Canal Mass: A Case Report Ear Sac Tumor Presenting as an External Ear Mass: A Case

Background: Endolymphatic sac tumor is a rare, aggressive, locally destructive lesion of the skull base that may be sporadic or associated with von Hippel-Lindau disease. It commonly presents as a bluish mass behind an intact tympanic membrane. This report describes a rare case of endolymphatic sac tumor presenting as a mass in the external ear canal. Case: A 57-year-old female patient presented with a history of progressive unilateral hearing loss and recurrent otorrhea in the right ear for 4 months. Physical examination revealed a mass bulging from the posterior external ear canal. Computed tomography showed an enhancing soft-tissue density lesion in the right external ear canal with minimal bony erosion, including a fluid-filled right mastoid air cell and middle ear cavity. Surgical removal was performed, and the final pathologic results were consistent with aggressive papillary middle ear tumor. Discussion: Endolymphatic sac tumors originate from the endolymphatic epithelium and are characterized by a locally aggressive papillary growth pattern with bone destruction. The presentation is variable, but histological examination and immunohistochemical staining will aid in the diagnosis. Surgical removal is the treatment of choice. Immunohistochemical tests were positive for epithelial membrane antigen, S100, and AE1/AE3 and negative for thyroid transcription factor 1, chromogranin, and synaptophysin.At follow-up, the patient reported improvement in right-sided hearing loss. Microscopic examination revealed normal mucosa of the middle ear and mastoid cavity without tumor recurrence. The postoperative audiogram showed minimal improvement of hearing in the right ear (moderately severe mixed hearing loss). Follow-up examinations were performed every 2 weeks to evaluate the right middle ear and mastoid cavity. Postoperative CT at 6 months found no evidence of tumor recurrence. Of note, no abnormalities were visualized in the endolymphatic sac region. Annual CT was planned as a surveillance tool.


Introduction
Endolymphatic sac tumor (ELST) is a rare lesion of the skull base, the origin of which has recently been ascertained. Although most adenomatous tumors of the temporal bone are benign lesions of the mucosa of the middle ear, aggressive, locally destructive tumors have been reported. In 1988, Gaffey, et al. [1] reported 10 cases of an aggressive papillary middle ear tumor (APMET) characterized by a locally aggressive papillary growth pattern, bone destruction, and frequent endolymphatic sac invasion, which was established as an entity separate from middle ear adenoma. In 1989, Heffner [2] reported 20 cases of a tumor identical to that reported by Gaffey, et al. and proposed an endolymphatic sac origin. The origin of APMET in the endolymphatic sac was based on histological similarity between the tumor and normal endolymphatic sac epithelium.
According to the World Health Organization tumor classification (2005), ELST is synonymous with Heffner tumor and APMET [3].
The endolymphatic sac is derived from neuroectoderm and is located subjacent to the posteromedial surface of the temporal bone. This anatomic location explains the potential extension of the tumor. At the early stage, the tumor is located within the endolymphatic sac. At the later stage, it destroys much of the petrous bone, including the middle ear, and extends to the posterior fossa, reaching into the cerebellopontine angle. Despite the controversy about the origin of APMET, current evidence suggests that it is ELST with extension to the middle ear [4,5]. ELSTs are known to occur DOI: 10.26717/BJSTR.2020.31.005060 23981 more frequently in patients with von Hippel-Lindau (VHL) disease, but the presence of VHL disease is not required for the diagnosis, because sporadic occurrence is common. Patients with VHL disease are more likely to have bilateral ELSTs [6][7][8][9][10]. Here we report a rare case of APMET, with clinical, radiological, histological, and immunohistological findings.

Case Report
A 57-year-old female patient presented with a history of progressive unilateral hearing loss and recurrent otorrhea in the right ear for 4 months. On examination, a smooth, pinkish mass bulging from the posterior external ear canal was seen in the right ear. The right tympanic membrane could not be evaluated due to mass occlusion. Examination showed that the left ear was intact.
The audiogram showed severe mixed hearing loss in the right ear. Computed tomography (CT) showed an enhancing soft-tissue density lesion in the right external ear canal, with minimal bony erosion, including a fluid-filled right mastoid air cell and middle ear cavity without intracranial extension ( Figure 1). Magnetic resonance imaging was offered to the patient as a valuable tool for distinguishing the disease preoperatively, but it was not performed due to the patient's claustrophobia.

Discussion
ELSTs are rare, locally aggressive papillary tumors of the petrous bone, which may be sporadic or associated with VHL disease [11], an autosomal dominant disorder. These tumors tend to be bilateral when associated with VHL disease, but they can occur rarely in individuals who do not have mutations or deletions of the VHL gene [8]. Their origin is controversial, but, as the name suggests, they are thought to arise from the endolymphatic sac. Other possible sites of origin include the epithelia of the middle ear and the mastoid air cells [12]. ELSTs were grouped with adenomatous tumors of the middle ear until 1984, when Hassard and colleagues described an extradural papillary lesion that was adherent to the endolymphatic sac [13]. In 1989, Heffner reviewed the light and electron microscopic and immunohistochemical features of 20 papillarycystic tumors of the petrous bone and concluded that they were low-grade adenocarcinomas likely of endolymphatic sac origin [2].
Although these tumors do not typically metastasize, a recent case report by Bambakidis, et al. showed that they can metastasize to distant sites [14].
The tumor affects adults of both sexes from 17 to 71 years of age. The clinical prodrome is prolonged. The most common symptoms are hearing loss, otalgia, tinnitus, vertigo, and facial weakness [15]. Examination typically reveals a red or blue tumor just behind the tympanic membrane. Our patient presented with an unusual case of a mass bulging from the external ear canal. The and hence surgical removal is the treatment of choice, although complete resection may not be possible [14]. Patients may require further surgery to resect recurrent disease, and therefore follow-up imaging has an important role in tumor surveillance. Radiotherapy has been used for inoperable tumors, but its use is controversial [15].
To the best of our knowledge, ELST located behind the tympanic membrane has not previously been described. In our patient, the tumor was located in the posterior external ear canal with lytic lesion and chronic mastoiditis on CT. The differential diagnosis includes cholesteatoma, squamous cell carcinoma, and necrotizing otitis externa, but microscopic examination and immunohistochemical staining will help to distinguish these diseases.

Conclusion
ELST is a rare skull base tumor originating from the endolymphatic epithelium within the vestibular aqueduct, which is characterized by a locally aggressive papillary growth pattern with bone destruction. The presentation is variable, but histological examination and immunohistochemical staining will help to diagnosis the disease. Surgical removal is the treatment of choice.

Conflicts of Interest
The author declares that I have no conflicts of interest.