Microhemorrhage, a possible mechanism for cyst formation in vestibular schwannomas

OBJECT

Cystic vestibular schwannoma (VS) is a unique subgroup of VSs characterized by unpredictable expansion of the cyst component. Little is known, however, about the mechanism of cyst formation. In this study the authors compared neuroimaging and histological characteristics of cystic with solid VS to determine the pathogenesis of the cystic subgroup.

METHODS

Two cohorts, one comprising 10 patients with cystic VS and the other comprising 10 patients with solid VS, were studied. Surgery was chosen as the primary treatment in all patients, with no other modality applied. Preoperative magnetic resonance images and histological characteristics of the tumor in patients with cystic VSs were evaluated and compared with those in the group with solid VSs. Differences between the two groups were assessed using the chi-square test. Neuroimaging findings revealed that either fluid-fluid level or hemosiderin deposit was present in all cystic VSs. Histological evidence of microhemorrhage, such as hemosiderin-laden macrophages (p = 0.069), hemosiderin deposits (p = 0.019), thrombotic vessels (p = 0.008), and abnormal vessel proliferation (p = 0.006) were more prominent in cystic VSs compared with solid ones. There was no difference in Antoni type dominance and Ki-67 proliferative index between the two groups.

CONCLUSIONS

Intratumoral microhemorrhage is a possible mechanism of pathogenesis in cystic VS.

Multicystic acoustic schwannoma with intratumoral hemorrhage: a report of two cases

We encountered two multicystic acoustic schwannomas with intratumoral hemorrhage. The radiological appearance in each case was similar to that obtained with CT and MRI. From a histological perspective, in each case we observed hypervascularity with thin-walled, dilated vessels in clusters and hemosiderin depositions around the dilated vessels.

Multicystic acoustic neurinoma: report of two cases

A report of two unusual and remarkably similar cases of multicystic acoustic neurinoma in 46 and 60 year old patients is presented. The clinical presentation mimicked a regular acoustic neurinoma. The tumours in each case were similar in their radiological appearance. The entire tumour had a honeycomb appearance with well defined and multiple cysts. Each cyst contained xanthochromic fluid. Like in any other cystic acoustic neurinoma, the presence of multiple cysts made internal decompression of the tumour relatively easy but the dissection of the tumour from the adjoining cranial nerves was difficult. The pathogenesis of multiple cysts is analyzed and the literature on this subject is briefly reviewed.

Cystic acoustic neurinomas: studies of 14 cases

Cystic acoustic neurinomas (ANs) are less frequent and are different from solid ANs in clinical and radiological features. We had 14 cystic ANs (13.5% of 104 cases) in the last 17 years. Computerized tomographic or magnetic resonance images allowed for the classification of these cystic ANs into three types: Type A being large single cysts with a thin tumourous wall (7 cases); type B single cysts with a thick tumourous wall (3 cases); type C multicystic (4 cases). Half of the cystic ANs were not accompanied by enlargement of the internal auditory canal, despite the largeness of the cysts. The mean size of the tumours was 29 mm in diameter. Type A cysts had a shorter clinical history than types B and C. One patient had intact hearing. In five cases, an atypical initial symptom such as facial pain, dysgeusia, facial palsy, unsteadiness or vertigo presented. The trigeminal nerve was involved in 12 cases, the facial nerve in nine. The characteristic features of cystic ANs are largeness of the tumour, a short clinical history, an atypical initial symptom, facial nerve involvement, and/or no enlargement of the internal auditory canal. In addition, the histological features are a lobular growth pattern, high nuclear atypia, and numerous macro phages.

Cystic vestibular schwannomas: neuroimaging and growth rate

In a series of 571 vestibular schwannomas (VS) operated on in the period 1976-1992, via the translabyrinthine approach, 23 tumours (4 per cent) from 23 patients were radiologically, peroperatively and histologically identified as cystic VS. Neuroimaging examinations (CT and MRI) revealed 15 tumours (2.6 per cent) with extracystic formations and in eight cases (1.4 per cent) intratumoural cysts. In 15 cases (65 per cent), tumours were located extracanalicularly with no involvement of the internal auditory canal (IAC). The extracanalicular tumour extension including the cystic elements ranged between 10 and 60 mm with a mean of 45 mm. In eight cases out of 23 (35 per cent) other diagnostic possibilities such as trigeminal schwannoma, epidermoid cyst and meningioma were proposed at the primary evaluation. Deformation, displacement and/or impression of the fourth ventricle was demonstrated in 17 cases (74 per cent). Three patients (13 per cent) had obstructive hydrocephalus which demanded shunt insertion. Residual tumour was detected in two patients (9 per cent). Growth rate in four cases was more than 10 times higher when compared to the annual growth rate of noncystic VS. The results of this study provide data on cystic VS attenuation demonstrated by CT or MRI which may be valuable in neuroradiological diagnosis of these cystic lesions and emphasizes that the wait-and-see policy should not be applied to the cystic variant of VS.

Histology and neuro-imaging in cystic acoustic neuromas

Tumor configuration and attenuation on CT scan with contrast enhancement or gadolinium-DTPA-enhanced MR depends upon tumor histology. Various elements are responsible for the density on CT or MR, e.g. blood vessels, fatty tissue, connective tissue, calcium, necrotic tissue, hemorrhage and intra- or extratumoral cyst formation. In a series of 571 acoustic neuromas we found 23 cystic tumors. The diagnosis was based on neuro-imaging examination, confirmed at surgery and finally verified histologically. Eight tumors with small or large cysts were diagnosed by CT or MR scan as intratumoral, and 15 with large cysts were diagnosed as extratumoral. We found a good correlation between the histology of cystic acoustic neuromas and the CT or MR scans. The tumors were predominantly hypodense, corresponding to the cystic areas, but also iso- or hyperdense areas were observed, corresponding to other tissue types. Antoni type B tissue and xanthomatous areas were found in all 23 cases.