Surgical Treatment of an Endolymphatic Sac Tumor

Summary

Here, we discuss clinical and radiological features of endolymphatic sac tumors and report the methodology and results of a surgical removal in a case in care at our otologic referral center.

Abstract

Endolymphatic sac tumors (ELST) are low-grade papillary adenocarcinoma originating from the endolymphatic sac. Usually slow-growing, with local aggressiveness and a low risk of distant metastases, ELST can be sporadic but also frequently associated with von Hippel Lindau disease. The current treatment of ELST is primarily surgical resection. A 55-year-old woman accessed our otologic tertiary level referral center for a sudden worsening of hearing loss in her left ear and vertigo. A magnetic resonance (MRI) and computer tomography scan study subsequently showed a mass in the petrous bone; hence, the presence of an ELST was hypothesized. After embolization of the mass, the patient underwent surgical removal of the lesion. The resection of the mass was done through a translabirinthine approach, with an uneventful procedure. No residual disease remained after surgery. After 24 months of radiologic follow up with MRI, there are no signs of recurrence disease. This paper reports the management of this sporadic ELST, as well as the follow up results, providing clinicians this protocol for the handling of such a challenging otologic skull base surgery and rare disease.

Introduction

Endolymphatic sac tumors (ELST) are neoplasms originating from the endolymphatic sac, a neuroectoderm-derived organ located in the posteromedial surface of the temporal bone. Histologically, ELST are characterizable as low-grade papillary adenocarcinoma¹. Usually, ELST are slow-growing, with local aggressiveness and a low risk of distant metastases^2,3,4. ELST can be sporadic, but they are also frequently associated with von Hippel Lindau disease (VHL)⁴.

Given the slow growing rate, the paucity of the clinical signs, and the late onset of the symptoms, they are difficult to diagnose in the early stages, especially when not associated with VHL^5,6. The typical symptomatology at diagnosis of ELST includes hearing loss (79.8%), tinnitus (52.6%), and disequilibrium (45.5%), due to endolymphatic hydrops or intralabyrinthine hemorrhages^4,7,8. Further and less frequent symptoms are facial palsy (25.6%), headache (13.8%), otalgia (5.1%), and trigeminal symptoms (3.2%)⁸.

The current treatment of ELST is primarily surgical resection. The tumor's residuals can be treated with stereotactic radiosurgery, which can be considered if the patient cannot tolerate the operation^9,10. The surgical approach and the prognosis are mostly related to the tumor extension⁶. Even if there is no official staging system for ELST^11,12, a recent grading system proposed by Li and colleagues¹³, based on imaging data and intraoperative findings, defined four main grades, according to the tumor extension. This and other previously proposed staging systems are reported in Table 1.

Article	ELST Staging / Grading
Bambakidis et al.11	Stage I: confiled to the temporal bone and middle ear
	Stage II: extended to the posterior fossa
	Stage III: extended to the middle cranial fossa
	Stage IV: extended to the clivus and/or sphenoid wing
Schipper et al.12	Type A: limited to the dura of the posterior cranial fossa
	Type B: infiltration of lateral semicircular canal and/or cochlea
	Type C: infiltration of sigmoid sinus and/or jugular bulb
Li et al.13	Grade I: confined to the posterior petrous bone between posterior semicircular canal and posterior fossa, may involve facial nerve, no inner ear and jugular foramen invasion
	Grade II: extended anteriorly with invasion of semicircular canals, cochlea, IAC, middle ear, without cerebellopotine angle and jugular foramen involvement
	Grade IIIa: involvement of jugular foramen or internal carotid artery or clivus
	Grade IIIb: extensive intracranial invasion or involvement of cavernous sinus or jugular foramen
Wu et al.6	Type I: confined to the endolymphatic sac region
	Type II: extended to at least another one anatomic structure

Table 1: Previously published tumor staging systems. An overview of previously published grading/staging systems.

To date, only ~300 cases were reported, mostly as single clinical cases or small case series^5,6. Recurrence rates and survival estimates have not been clearly defined yet⁸. In the present paper, we report the clinical and surgical management of a single case of sporadic ELST, as well as the follow-up results, providing clinicians our experience of the handling of such a challenging otologic skull base surgery and rare disease. Here, we describe ELST in a 55-year-old woman who accessed our otologic tertiary level referral center from a peripheric hospital. The patient had been hospitalized 3 days before for a sudden worsening of the left hearing loss, which began 3 months earlier, accompanied by an episode of acute vertigo with nausea and vomiting. The anamnesis was positive for hypertension and hypercholesterolemia, both under treatment, and smoking (3 pack-years). No personal or familiar history of VHL disease or compatible symptoms were reported by the patient.

Protocol

The local ethical committee approved the publication of this clinical case. A written informed consent form was collected from the patient.

1. Clinical and audiological evaluation

1. Collect personal or familiar history of VHL disease or compatible symptoms from the patient.
2. Perform a neurological examination to investigate central causes. Ensure that there is no pathological cause to be underlined and the facial nerve function is normal.
3. Assess external, middle, and inner ear functionality and assess whether a complete audiological and otoneurological evaluation is necessary.
4. After a bilaterally negative otoscopy, perform a hearing assessment using a pure tone and vocal audiometry with a classical clinical audiometer and a tympanometry with stapedial reflex study with a clinical tympanometry.

2. Imaging study

1. Perform an MRI to further exclude other causes of vertigo and to study the internal auditory canal (IAC) and pontocerebellar angle (PCA), 2 days after the hospitalization.
   1. Use a 1.5 T MRI system equipped with an 8-channel phased array head coil to perform the brain, brainstem, and petrous bone examination.
   2. For the MRI examination protocol, use axial fluid-attenuated inversion recovery and axial fast spin-echo T2-weighted sequences. Target steady-state free precession (SSFP) images with a FIESTA (Fast Imaging Employing Steady-state Acquisition) sequence on the inner ear. Acquire high-resolution volumetric images with T1-weighted SPGR (Spoiled Gradient-Recalled) sequence before and after contrast media administration.
2. Perform a high-resolution computer tomography (HRCT) of the petrous bone, with a 64-slice scan to confirm the presence of any isodense mass.
3. After the execution of the MRI and the HRCT, define the grading of the tumor and plan the surgical approach for the mass resection. Discuss the prognosis of the surgery and the disease with the patient.

3. Surgical management

1. Twenty-four hours before the surgery, have an experienced interventional neuroradiologist perform an arterial embolization of the mass on a biplane angiograph.
2. Perform the embolization with poly vinyl alcohol particles of 150-250 microns size with selective catheterization of the feeding vessels.
3. If as in this case, there is limited extension of the tumor but a relevant hearing deficit, schedule a surgical resection of the mass through a translabirinthine approach to be performed by a 25 years-experienced surgeon of the ear and the lateral skull base.
4. After a C-shaped retroauricolar incision and the raising of a temporalis muscle's flap, perform an ample mastoidectomy with a Striker S2 πDrive drilling system.
   1. Cut round precision and fluted tips, as well as coarse and fine diamond round tips, depending on the drilled structures.
   2. Expose the sigmoid sinus and the dura of the middle cranial fossa posteriorly and superiorly, respectively.
   3. Complete an ample antrotomy with a complete exposure of the small process of the incus and then, prepare a posterior tympanotomy.
   4. Drill out all the retro-facial mastoid cells up to the mastoid tip, until the identification of the jugular bulb.
   5. Complete the posterior labyrinthectomy with semicircular canals until the identification of the internal auditory canal (IAC).
   6. Identify the neoplasm after the complete exposure of the dura of the middle and posterior cranial fossa, in the endolymphatic sac area. If the the neoplasm is indivisible from the dura of the posterior cranial fossa, cut the dura and remove it en-bloc with the tumor. If the neoplasm has reached and invaded the IAC, open the IAC to completely remove the tumor.
5. Conduct an intraoperative extemporaneous histological examination.
6. Seal the posterior tympanotomy and the antrotomy with surgical wax, and fill the ample mastoid cavity with autologous abdominal fat and fibrin glue.
7. Check for post-surgical cerebrospinal fluid (CSF) leak and assess the blood loss due to surgery.

4. Postsurgical course

1. In the post-operatory course, check for vertigo, residual hearing, CSF leakages, and facial nerve palsy among other complications.

Results

From the audiologic assessment, it was possible to identify a moderately severe left sensorineural hearing loss (Figure 1), with a reduction of word discrimination. The tympanometry was bilaterally normal, and the stapedial reflexes were evocable with ipsilateral and contralateral stimulus. At the videonystagmography , it was possible to assess a grade II horizontal spontaneous nystagmus beating on the right side, which grew in intensity after head shaking. From the clinical and audiological...

Discussion

ELST are rare and locally aggressive neoplasms that arise on the posteromedial surface of the temporal bone. Due to their slow growth rate, and the initial paucity of the symptoms, the diagnosis is often delayed, resulting in an advanced tumor stage. Since the surgery morbidity as well as the oncologic outcomes are strongly correlated with the tumor dimensions and extension^6,8,13,15, an early d...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
AC40	Interacoustic		Clinical audiometer
AT235	Interacoustic		Clinical tympanometry
Innova 3131	GE Healthcare		Biplane angiograph
LightSpeed VCT	GE Healthcare		64 Slice CT system
S2 πDrive	Striker		Drilling system for Otosurgery
Signa HDX	GE Healthcare		1.5 T MRI system
SYNAPSYS VNG	Inventis		Video nystagmograph