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 hemosiderinladen 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.

Point Mutation of neu Oncogene in Animal Peripheral Nerve Sheath Tumors

Thirty-four peripheral nerve sheath tumors of four domesticated animal species were characterized and assayed for point mutation of the neu oncogene. Based on their morphoimmunophenotype, 32 tumors were classified as schwannomas. Schwannoma morphology was characterized by the presence of Antoni type A and B pattern and immunoreactivity for S-100 protein and vimentin. Two anaplastic and metastatic tumors originating from spinal cord root, immunonegative for S-100 protein and positive for vimentin, were classified as malignant peripheral nerve sheath tumors (MPNSTs). Four malignant schwannomas and two MPNSTs expressed a point mutation of the neu oncogene by the polymerase chain reaction-restriction fragment length polymorphism method. The finding of neu oncogene mutation could be a useful diagnostic genetic marker in the malignant form of peripheral nerve sheath tumors in animals.

Spontaneous Cardiac Tumors in Eight Rats

Spontaneous cardiac neoplasms were diagnosed in one Sprague-Dawley and seven Fischer 344 rats ranging in age from eight months to two years. All eight neoplasms were diagnosed as neurilemmomas. One neoplasm was composed of dense Antoni type A tissue with Verocay body formation, while seven others were composed principally of loose Antoni type B tissue. No specific site predilection was found.

Intracanalicular Neurilemmomas Clinicopathologic Study

Twenty-five patients with intracanalicular neurilemmomas were studied, the largest series yet reported. The tumors were most frequent in men by a ratio of 2:1, occurred more often on the left acoustic nerve, were generally associated with long duration of symptoms, and were equally distributed in the third to fifth decades, but the prevalence slightly increased in the sixth and seventh decades. A shorter length of illness occurred in younger persons as well as most patients with von Recklinghausen's disease. The length of illness ranged from six months to 35 years. Symptoms generally were limited to the auditory nerve except in three instances of involvement of the facial nerve. These three cases were the only ones with preoperative facial palsy. Posterior fossa myelogram was the most useful diagnostic aid. The rate of growth in one patient was estimated to be 1 to 2 mm per year by serial study of myelograms, but the growth rate is probably variable. CT scans were not useful in detecting small tumors. Histologically, most tumors less than 1 cm in diameter were primarily composed of Antoni type A tissue. Vascular malformations were found within the tumor in three cases. Altered blood vessels are the mechanism whereby characteristic changes occur in the cerebrospinal fluid (CSF). Small tumors generally lack blood vessels, hence are less often associated with abnormal CSF.

The Ultrastructure of Bovine Peripheral Nerve Sheath Tumours

Bovine peripheral nerve sheath tumours from 30 cattle were similar ultrastructurally to human schwannomas and neurofibromas. Bovine neurofibromatous tissue had large amounts of extracellular material, primarily collagen and electron lucent granular material. The principal cells had basal laminae and a disorganized proliferation of the plasmalemma. Axons were consistently seen and were surrounded by the plasmalemma of principal cells. The principal cells seemed to be Schwann cells or variants of them. Bovine schwannomas had areas similar to Antoni type A tissue with sparse extracellular material, few, if any, axons, and an apparent organized layering of cytoplasmic processes clad in a basal lamina. Cell nuclei often formed palisades. The principal cells in bovine schwannomas might be derived either from Schwann cells or perineurial cells. Bovine schwannomas appeared together with bovine neurofibromatous tissue in affected nerves.