Oculomotor Nerve Schwannoma Presenting as an Entirely Cystic Homogeneous Mass on Magnetic Resonance Imaging: Case Report

Case Report

Austin Neurosurg Open Access. 2014;1(3): 1013.

Oculomotor Nerve Schwannoma Presenting as an Entirely Cystic Homogeneous Mass on Magnetic Resonance Imaging: Case Report

Suenaga J*, Tateishi K, Takase H, Kanno H and Kawahara N

Department of Neurosurgery, Yokohama City University Graduate School of Medicine, Japan

*Corresponding author: Suenaga J, Department of Neurosurgery, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, Kanagawa 236-0004, Japan

Received: April 29, 2014; Accepted: June 05, 2014; Published: June 09, 2014

Abstract

A 79–year–old woman presented with left oculomotor nerve paresis. Initial Computed Tomography (CT) demonstrated an isodense cystic lesion 15 mm in diameter in the left crural and carotid cisterns. On Magnetic Resonance Imaging (MRI), the cyst was homogeneously hyperintense on both T1– and T2–weighted imaging with slight hemorrhage. Removal of the lesion was indicated, since the cyst was gradually enlarging and symptoms were progressing. Since the cyst was tightly attached to the oculomotor nerve, partial resection was performed. Pathology of the cyst wall revealed schwannoma with microhemorrhage. However, the residual tumor showed sudden bleeding 1 month later, so second surgery was performed to remove the tumor subtotally, leaving a small piece of residual capsule tightly adhering to the brainstem and internal carotid artery. Although oculomotor nerve schwannoma is rare, particularly presenting as a completely cystic mass, this diagnosis should be considered with such lesions. In addition, total or subtotal resection to prevent further enlargement or hemorrhage might be indicated, even in older patients.

Keywords: Oculomotor nerve schwannoma; Cyst formation; Intratumoral hemorrhage

Abbreviations

CT: Computed Tomography; MRI: Magnetic Resonance Imaging; DWI: Diffusion–Weighted Imaging; VS: Vestibular Schwannoma; CSF: Cerebrospinal Fluid; EMA: Epithelial Membrane Antigen; GKR: Gamma Knife Radiosurgery; FLAIR: Fluid–Attenuated Inversion– Recovery

Introduction

Oculomotor nerve schwannoma in the absence of neurofibromatosis is extremely rare, with only 56 cases previously reported in the literature [1–8]. According to a systematic review by Furtado et al. [2], the most common site of origin is in thecisternal segment of the oculomotor nerve. Although radiological diagnosis is usually made by Magnetic Resonance Imaging (MRI), precise diagnosis is often difficult, and differentiation from other tumors, including meningioma, dermoid cyst, craniopharyngioma,neurenteric cyst, and pituitary adenoma, is warranted. We recently treated a patient with an entirely cystic schwannoma originating from the oculomotor nerve in the crural cistern, which showed rapid growth and intratumoral hemorrhage. Such cystic tumors are extremely rare, and only two cases have been reported [5,6]. We report this case and review the pertinent literature, with particular focus on the radiological features.

Case Presentation

A 79–year–old woman presented to our clinic with left oculomotor nerve paresis. No special past or family history such as neurofibromatosis was noted. Computed Tomography (CT) showed an isodense cystic lesion 15 mm in diameter in the left crural cistern (Figure 1A). Tiny high–density niveau in this mass suggested hemorrhage in the cyst. No calcification or vessel anomaly was seen on CT angiography. MRI also revealed a homogeneous cystic mass, hyperintense on both T1– and T2–weighted imaging (Figure 1B, C). The tumor capsule did not show clear contrast enhancement. The mass was isointense to brainstem on Diffusion–weighted Imaging (DWI). Due to the advanced age of the patient, we continued close observation; however, the cyst gradually enlarged and reached 22 mm in diameter after 6 months (Figure 2). The mass effect of the tumor on the left cerebral peduncle was increased, and oculomotor function gradually deteriorated. We finally decided to resect the tumor inorder to decompress the brainstem, based on a tentative preoperative diagnosis of neurenteric cyst.