A rare tumour in the cerebellopontine angle: endolymphatic sac tumour

We present a case of a papillary tumour at the cerebellopontine angle in a 54-year-old man. He presented with right-sided ear pain associated with dizziness and hearing loss. The radiological diagnosis was in favor of acoustic neurinoma. Surgical excision was performed and the diagnosis of the endolymphatic sac tumour was made. Endolymphatic tumour is a low grade adenocarcinoma that originates from the endolymphatic sac. The definitive diagnosis requires a combination of clinical features, radiological finding and pathological correlation.


Introduction
Endolymphatic sac tumor (ELST) is a rare neoplasm with benign histopathological appearance and clinically destructive behavior which occurs in the skull base and frequently invades the posterior petrous bone, the mastoid and cerebellopontine angle (CPA). It is synonymous with Heffner tumor, low grade adenocarcinoma of endolymphatic sac origin, and aggressive papillary middle ear tumor according to the recently published World Health Organization tumor classification [1]. It is extremely rare in the general population and has an association with Von Hippel-Lindau (VHL) disease [2]. Although the endolymphatic sac papillary tumor is a benign tumor, its growth pattern is often invasive [3]. We present a case of endolymphatic sac tumour in a 54-year-old man who was clinically and radiologically diagnosed as acoustic schwannoma and review the available literature on its clinicopathological and therapeutic features.

Discussion
Neoplasm arising from the endolymphatic sac was first described by Hassard [1]. Subsequently, the term low grade adenocarcinoma of endolymphatic sac origin was coined by Heffner in 1989 who found similarities in the anatomical location and histological features of the normal endolymphatic sac to this tumour [4]. A number of incorrect definitions such as primary middle ear adenoma, adenomatous tumors of the middle ear, adeno-cysto-carcinoma, choroidal plexus papilloma, have been applied subsequently to ELST [3]. ELST is reported to be more common in females with a mean presenting age of 45 years. Sensorineural hearing loss, tinnitus and vertigo are the typical presenting symptoms in patients with ELST as seen in our patient. Cranial nerve paralysis including facial nerve palsy and cerebellar disorders develops as the tumor extends into the jugular foramen and cerebellopontine angle [5]. This neoplasm behaves as a slow growing tumor which is locally invasive and exhibits bone destruction. Earlier reported cases of ELST showed no metastasis but recently ELST metastasis to the spine has been observed [6]. Rare cases of papillary meningioma have been reported in the temporal bone but they are cytologically anaplastic with areas of necrosis, pleomorphism, and high mitotic activity. Metastatic lesions to the temporal bone may cause difficulty in diagnosis but proper work up along with immunohistochemical stains will help to distinguish between the two [7]. The imaging studies reveal a destructive lesion of the petrous bone which is heterogeneous, space-occupying lesion arising from and invading the temporal bone and even extending into the posterior fossa. Other differential image diagnoses for ELST include acoustic neuroma, which could lead to the destruction of the petrous apex of the temporal bone [8] and compressing the cerebellum.
The present case showed a similar appearance in magnetic resonance imaging. Concerning treatment of this tumor, radical surgical local excision remains the mainstay of current therapy. The best treatment choice is the total removal of the lesion, which may sometimes necessitate sacrifice of cranial nerves, because total resection of the advanced tumors may be impossible due to the anatomic complexity [9], so postoperative radiotherapy was suggested as adjuvant therapy in most cases. Owing to their locally aggressive nature and difficult to extirpate surgically, local radiotherapy should be applied in time, depending on surgical excision status. In addition, radiotherapy may also be suitable as a salvage treatment in recurrent endolymphatic sac tumors [10].

Conclusion
ELST should be taken into consideration for differential diagnosis of CPA tumors. Detailed clinical and radiographic evaluation is required to direct an appropriate management in every case. Radical excision is feasible using appropriate surgical approach. Early diagnosis, surgical excision and long-term regular follow-up may constitute an efficacious management.

Competing interests
The authors declare no competing interests.

Authors' contributions
All the authors have contributed to this work in ways that comply to ICMJE authoship criteria. All the authors have read and approved the final version of the manuscript.