|Year : 2015 | Volume
| Issue : 1 | Page : 5-7
Endolymphatic sac tumor: A temporal rarity revisited
Anirudh V Nair1, CJ Sandya2, Srikanth Moorthy2, PV Ramachandran2, Zuhara Shemin3, Annie Jojo3
1 Department of Radio Diagnosis, Kerala Institute of Medical Science and Research Centre, Trivandrum, Kerala, India
2 Department of Radio Diagnosis, Amrita Institute of Medical Science, Kochi, Kerala, India
3 Department of Pathology, Amrita Institute of Medical Science, Kochi, Kerala, India
|Date of Web Publication||10-Mar-2015|
Dr. Anirudh V Nair
Department of Radio diagnosis, Kerala Institute of Medical Science and Research Centre, Trivandrum - 695 029, Kerala
Source of Support: None, Conflict of Interest: None
Endolymphatic sac tumor (ELST) is a rare cystadenomatous neoplasm with a benign histopathological appearance and a locally destructive behavior. ELST can produce clinical manifestations even when it's microscopic in size. The imaging hallmark of ELST is the presence of retrolabyrinthine mass associated with osseous erosion. Treatment of ELST involves local resection of the tumor or radical mastoidectomy, or in combination with radiotherapy.
Keywords: Endolymphatic sac tumor, High-resolution computed tomography temporal bone, Magnetic resonance imaging, Papillary adenocarcinoma
|How to cite this article:|
Nair AV, Sandya C J, Moorthy S, Ramachandran P V, Shemin Z, Jojo A. Endolymphatic sac tumor: A temporal rarity revisited. Indian J Otol 2015;21:5-7
|How to cite this URL:|
Nair AV, Sandya C J, Moorthy S, Ramachandran P V, Shemin Z, Jojo A. Endolymphatic sac tumor: A temporal rarity revisited. Indian J Otol [serial online] 2015 [cited 2019 Oct 16];21:5-7. Available from: http://www.indianjotol.org/text.asp?2015/21/1/5/152848
| Introduction|| |
Endolymphatic sac tumor (ELST) is a rare papillary cystadenomatous neoplasm centered at posterior aspect of the temporal bone, with benign histopathological appearance and locally destructive behavior. The orgin of ELST to endolymphatic sac was first attributed by Hassard et al., in 1984 and was subsequently confirmed on clinical, histological, electron microscopic and immunohistochemial grounds by Heffner. Although the tumor is encountered sporadically, they are also seen in patients with von Hippel-Lindau disease.
| Case Summary|| |
A 46-year-old male presented with a history of tinnitus and ear block in the right ear since last 14 years. Consulted at local hospital and had been on symptomatic treatment. There was a progressive loss of hearing on the right side with difficulty in localizing sounds since last 8 years. He developed unsteadiness of gait since 6 years, with swaying towards the right. Since the last 2 years, he developed sensory impairment over the right side of his face with difficulty in swallowing. He also has associated change in voice, difficulty in holding objects tightly, history of dropping objects, and involuntary spastic movements over the right side of the face. On clinical examination, he had decreased sensation along the distribution of cranial nerves V2 and V3 on the right side. He had 7 th nerve and 8 th nerve palsy also on the right side.
Computed tomography (CT) brain and high-resolution CT temporal bone with contrast showed a large destructive lesion in the retrolabrynthine temporal bone extending into the cerebellopontine angle cistern on right side [Figure 1]a and b. Posterior wall of internal auditory canal was destroyed. Cochlea, semicircular canals, and middle ear ossicles were normal. Descending facial canal was eroded and encroached by the mass. Sigmoid plate, jugular fossa, mastoid air cells and posterior wall and floor of middle ear showed erosion. The exophytic component in cerebellopontine angle appeared cystic in density and showed peripheral rim enhancement with mass effect on the right cerebellar hemisphere, pons, and fourth ventricle.
|Figure 1: (a) High-resolution computed tomography (CT) axial image, large osseous destructive lesion in the right retrolabrynthine temporal bone. Destructed endolyphatic canal on the right as compared to normal canal on left (arrow head), (b) contrast enhanced CT axial, showing exophytic cystic component in cerebellopontine angle with peripheral rim enhancement and mass effect (arrow)|
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Magnetic resonance imaging (MRI) showed the mass to be intermediate signal at T1-weighted, and appearing hyperintense on T2-weighted images with enhancing soft tissue component in postcontrast T1-weighted fat sat images [Figure 2]a-c.
|Figure 2: Magnetic resonance imaging axial T1-weighted: (a) Shows hypointense lesion on right temporal bone and (b) appearing hyperintense on T2-weighted images, (c) enhancing soft tissue component of postcontrast T1-weighted fat-sat images|
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Patient was subsequently taken up for excision via transcochlear approach. Histology was reported as low grade papillary adenocaracinoma of endolymphatic sac (ELS) [Figure 3]a-d and was planned to be followed-up without radiotherapy.
|Figure 3: (a) Scanner view showing papillary adenocarcinoma (arrow head), (b) high power view showing papillae, (c) immunohistochemistry showing pan-cytokeratin positive, (d) ×10 view showing through and through bony invasion (arrow)|
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| Review of Literature|| |
Endolymphatic sac tumor (ELST) is a rare papillary, cystadenomatous neoplasm centered at posterior aspect of the temporal bone, with benign histopathological appearance, locally destructive behavior  and frequent intracranial extensions.
Though the site of orgin is still controversial,  its believed that they arise from the complex rugose portion of the ELS, which extends from its intraosseous origin to intradural extra osseous terminus. 
Endolymphatic sac tumors are seen more frequently in patients with von Hippel-Lindaeu (VHL) disease, with up to 16% of patients with VHL disease harboring an ELST  Patients with VHL disease are more likely to have bilateral ELST. Though these tumors do not metastasize, single case report of spinal metastasis is reported in the literature.  Hence, this tumor must be distinguished from other benign tumors of the middle ear and temporal bone.
Endolymphatic sac tumor produce symptoms even when microscopic in size and can lead to symptoms such as hearing loss, tinnitus, vertigo, and facial nerve dysfunction.
| Anatomy of Endolymphatic Sac|| |
Vestibular aqueduct is a bony channel originating from the posterosuperior portion of the vestibule near the common crus. It courses posteriorly, laterally and inferiorly along the posterior petrous surface. The vestibular aqueduct widens as it approaches its external aperture at the posterior margin of the petrous apex. The length of vestibular aqueduct is generally 6-12 mm and vestibular aqueduct is considered large when it measures > 1.5 mm at mid-point between the common crus and the aperture. Vestibular aqueduct houses the endolymphatic duct system (EDS). EDS is divided into an endolymphatic duct (ELD) and ELS. ELD contains endolymph and is bathed in perilymph. ELD is also surrounded by loose connective tissue which is continuous with the adjacent periosteum [Figure 4].
Histologically the lining epithelium of ELD is similar to utricular and saccular ducts and is composed of simple squamous or low cuboid cells. ELD terminates as ELS. ELS has a proximal (rugose) intradural portion and distal (smooth) small intraosseous portion. Proximal ELS consists of a complex network of interdigitating canaliculus and crypts lined by highly differentiated epithelium. The distal segment of ELS is lined by cuboid epithelium and situated between the periosteal portion of dura and dura proper.
Endolymphatic duct and ELS play a role on autoregulation of the inner ear and fluid balance. Arterial supply orginates from the dural branch of the stylomastoid artery arising from the occipital or posterior auricular artery.
| Imaging Protocol for Endolymphatic Sac|| |
HRCT of temporal bone at 0.625 mm slice thickness can be used for detailed evaluation of anatomy and pathological process affecting temporal bone and inner ear. VA is visible on high resolution computerized tomography (HRCT) of temporal bone.
There is steep angulation of long axis of ELS, making nearly 70 degrees with the infraorbital-meatal line.  MR-multiplanar reformatted images parallel to the plane of vestibular aqueduct, reformation at double oblique angle 45 degree from true sagittal and 70 degree from orbital-meatal line, is useful to view the entire ES/VA on one section giving a "Christmas tree" appearance. 
Internal architecture of cochlea is better seen on FIESTA MRI than on CT. However, the normal VA is faintly seen on FIESTA in contrast to FSE T2W, where it appears hyperintense. VA and cochlear duct can also be imaged with 3D-CISS sequence.
| Imaging Characteristics|| |
The imaging hallmark of ELST is the presence of retrolabyrinthine mass associated with osseous erosion. CT demonstrates an expansile lytic lesion of the retrolabrynthine and mastoid process of the petrous bone, which may extend to involve the posterior fossa and middle ear.
Magnetic resonance imaging shows the core of the tumor as isointense with brain on both the T1-and T2-weighted images with a slight enhancement after intravenous gadolinium.  There are four potential vectors for ELST extension: Posteromedially into the cerebellopontine angle, laterally toward the middle ear, superiorly toward the middle cranial fossa, and anteromedially along the petrous ridge toward the cavernous and sphenoid sinuses. 
Differential diagnosis to be considered in a suspected case of ELST includes destructive lesions of the temporal bone such as paraganglioma, meningioma, hemangiopericytoma, and metastases. 
| Management|| |
Treatment of ELST involves local resection of the tumor or radical mastoidectomy, or in combination with radiotherapy. Early surgical excision is the best option when the tumor is small. When the tumor is large, complete excision is nearly impossible due to the anatomic complexity of the ELS and distinct patterns of tumor extension. Radiotherapy may be the only option in advanced cases although there are no studies focusing on the role of adjuvant radiotherapy on advanced ELST. Because ELST is richly vascularized, some scholars suggest that preoperative embolization may be helpful. Local recurrence can occur.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]