Hemorrhagic Vestibular Schwannoma: Case Report and Literature Review of Incidence and Risk Factors

Hemorrhagic vestibular schwannoma (HVS) consisting of acute intratumoral and subarachnoid hemorrhage presents with acute nausea, vomiting, facial numbness, headache, loss of consciousness, and significant functional impairment of the facial and vestibulocochlear nerves. The current case is of a 31-year-old man who was presented with acute left lateral suboccipital headache, vomiting, ataxia, and loss of consciousness. Brain CT revealed a large iso-intense lesion with internal hematoma at the left cerebellopontine angle in association with internal acoustic canal dilation. In addition, MRI confirmed a 32 x 25 x 26 mm vestibular schwannoma (VS) with 20 x 15 x 5 mm intratumoral hematoma. The patient had undergone left lateral suboccipital craniotomy and microscopic tumor resection. Pathological findings revealed that his lesions were VS. The average incidence of HVS is around 2.15 cases per year worldwide. Therefore, HVS incidence in proportion to VS is very low and consequently rare.


Introduction
had also developed deep vein thrombosis and pulmonary emboli 18 months ago and had used aspirin after thrombolytic therapy. Moreover, he had a history of surgical removal of lung hydatid cyst 12 months ago as well as a history of headache for three years, which was intractable to any treatment. His prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR) were normal, and no abnormal findings were reported in lab results.
Brain CT revealed extra-axial lesion at the left cerebellopontine angle (CPA) region with an intralesion hematoma that expanded tumor volume ( Figure 1A). The left internal acoustic canal (IAC) was dilated in comparison with the right side. The brain stem and fourth ventricle were compressed with the mass effect of hemorrhagic tumor. There was some ventriculomegaly but no periventricular edema and hydrocephalus. In the MRI, 32 x 25 x 26 mm VS at the left CPA with extension to IAC was seen. The lesion was hypo-and hyperintense on T1-weighted image (T1WI) and T2-weighted image (T2WI), respectively ( Figures 1B-1D) and enhanced dens homogenous on contrast T1WI ( Figures 1F, 1G). Intralesion hematoma measuring 20 x 15 x 5 mm was iso-and hypointense on T1WI and T2WI, respectively, without T1WI enhancement contrast ( Figure 1).
The patient was operated at semi-lateral supine position with left lateral suboccipital craniotomy and microscopic retrosigmoid approach. Intratumoral hematoma was seen during tumor resection. The tumor was totally resected, and the facial nerve was preserved. The patient's postoperation course was uneventful and without any new neurological deficit (Figures 2A, 2B).

FIGURE 2: Lesion Microscopic View
(A) Low power field. (B) High power field microscopic view shows vestibular schwannoma. Antoni A and B patterns are seen in the collagenous background. In the hypercellular Antoni A areas, intersecting fascicles consisting of spindle cells with buckled nuclei are seen. These cells form Verocay bodies with nuclear palisading, making alternating bands of nuclear and anuclear areas. In the hypocellular Antoni B areas, the prominent myxoid extracellular matrix takes the spindle cells apart.
In the hematoxylin and eosin (H & E) staining, hypercellular (Antoni A) and hypocellular (Antoni B) areas are seen. Dense Antoni A areas consisting of interlacing bundles of spindle cells with oval nuclei, eosinophilic cytoplasm, and indistinct cytoplasmic borders are also seen. Hypocellular dense Antoni B areas are composed of haphazardly arranged spindle cells in loose myxoid collagen fibers. Blood vessels with hyalinized walls were visible.

Discussion
The VS is an uncommon intracranial tumor and frequently presents with chronic hearing loss, headache, tinnitus, disequilibrium, and facial numbness, whereas acute overt hemorrhage including subarachnoid hemorrhage (SAH) and ITH as its first presentation is quite rare [11].
Of all intracranial hemorrhages, 1-11% belong to hemorrhagic brain tumors. SAH that arises from brain tumors accounts for 0.4% of all cases of SAH. Furthermore, 1.7-10% of brain tumors cause intracerebral hemorrhage [12]. ITH generally occurs in 11% of all cranial tumors, and its occurrence in glioblastoma multiforme, pituitary adenomas, choriocarcinomas, oligodendrogliomas, choroid plexus papillomas, and meningiomas is also prevalent.
According to Mathkour et al.'s literature review, there were only 48 cases of VS secondary to ITH, whereas in accordance with our review of the literature ( Table 1), there were 97 HVS cases since 1974 including our case [13].
Based on the reported cases, the average incidence of HVS worldwide is approximately only 2.15 cases per year; therefore, HVS is a quite rare entity among VS tumors.
Some studies have reported hemorrhagic cystic VS (CVS) and therefore it can be considered as a risk factor for HVS ( Table 1). Although our case's tumor was not of cystic type, CVS has been characterized with faster expansion rate than the solid ones, rapid nerve involvement, and development of variable symptoms. CVS is more commonly demonstrated with fluid-fluid levels and hemosiderin deposition on imaging. Moreover, it has been argued that ITH can result in the formation of the cyst [14].