In the CNS, there are multiple isozymes of the sodium and potassium ion-stimulated adenosine triphosphatase (Na,K-ATPase) that have differences in affinity for Na+, ATP, and cardiac glycosides. Three forms of the catalytic subunit (designated alpha 1, alpha 2, and alpha 3) are known to be derived from different genes, but little is known of the cellular distributions of the proteins or their physiological roles. Isozyme-specific monoclonal antibodies permitted the immunofluorescent localization of the 3 Na,K-ATPases in the rat CNS, and markedly different patterns of staining were seen. All 3 isozymes were detected, singly or in combination, in 1 or more neuronal structures, while both alpha 1 and alpha 2 were detected in glia. Many different neuroanatomic structures or cell types stained for more than 1 isozyme. Even when a structure or region stained for more than 1 isozyme, the pattern of staining was frequently dissimilar, suggesting complex differences in gene expression and cellular localization.

Atypical teratoid/rhabdoid (AT/RT) tumor is a rare, highly malignant tumor of the central nervous system (CNS) most commonly found in children less than 5 years of age. Although the vast majority of cases are diagnosed in young children, there have been isolated case reports in adults. Since its histological appearance can be confused with other tumors, especially in adults, separating AT/RT from other neoplasms may be difficult. In many instances, a reliable diagnosis is not possible without demonstrating the lack of nuclear INI1 protein expression by immunohistochemical methods. The patients (three males and one female) ranged in age from 23 to 42 years (mean age, 32 years). Radiographically, two tumors were localized in the right fronto-parietal region, one was frontal and the other was found in the left temporal lobe. Varying degrees of hydrocephalus and heterogeneous enhancement were present on MRI. In all cases, diagnosis during intraoperative consultation and preliminary diagnosis was different from the final diagnosis after immunohistochemical analysis. Immunohistochemical staining showed that the tumor cells were positive for vimentin and reacted variably for keratin, epithelial membrane antigen (EMA), synaptophysin, neurofilament protein, CD34, and smooth muscle actin (SMA). All were negative for GFAP, S-100, desmin and CD99. Three of the four cases lacked nuclear expression of INI1. One patient is alive with no evidence of disease 17 years after the diagnosis. In adult examples of AT/RT, the diagnosis requires a high index of suspicion, with early tissue diagnosis and a low threshold for investigation with INI1 immunohistochemistry to differentiate this entity from other morphologically similar tumors. Although the prognosis is dismal in pediatric population, long term survival is possible in adult AT/RT cases after surgery and adjuvant radiotherapy and chemotherapy.

An aneurysmal dissection of a right middle cerebral artery (MCA) branch is described in a 56-year-old woman. The abnormality was an incidental finding on computerized tomography and subsequently appeared on magnetic resonance imaging performed to evaluate the patient for subjective pulsatile tinnitus. The intracranial aneurysm was documented to have enlarged on serial angiography over a 6-week interval. Treatment was believed to be necessary because of the unknown etiology of the aneurysm, with the differential diagnosis including mycotic or neoplastic aneurysm with a risk of hemorrhage. The lesion was excised and flow to the distal MCA branch was preserved with an anastomosis of the superficial temporal artery to the MCA. The aneurysm, which developed at the level of the sylvian fissure, proved on pathological study to be related to a focal dissection of the MCA branch. The radiographic appearance and pathological findings are presented. Focal dissection must henceforth be included in the differential diagnosis of peripheral cerebral artery aneurysms.

Three genetically distinct isozymes of the catalytic subunit of the Na,K-ATPase have been detected and have been designated alpha1, alpha2, and alpha3. To determine whether their expression is restricted to identifiable neurons and glia, specific monoclonal antibodies were used for immunofluorescent localization in the rat retina and optic nerve. The patterns of staining were markedly different, suggesting differences in cellular localization. Photoreceptor inner segments and optic nerve fibers expressed predominantly alpha3. Müller glia in the retina and astrocytes in the optic nerve expressed alpha1 and alpha2. Isolated, dissociated bipolar, horizontal, and Müller cells expressed different isozymes separately or in combination. The complexity of staining of neurons and their axons and dendrites suggested that Na,K-ATPase isozyme expression is not stereotyped, but is tailored to the ion transport needs of individual cell types, and targeted to specified membrane domains.