Hidehiro Takei

Metastases are the most common brain tumors especially in adults. Although they are generally considered a single disease entity which is universally fatal in patients with advanced cancer, brain metastases are remarkably heterogeneous both clinically and pathologically. As members of the multidisciplinary clinical team for the diagnosis and management of metastatic brain tumors, pathologists must be familiar not only with clinicopathologic features of brain metastases but also with any characteristic and clinically significant molecular findings. We discuss here the epidemiology, general gross and microscopic features of brain metastases with emphasis on how to differentiate them from primary brain tumors using immunohistochemistry (e.g., for identification of the primary site and differential diagnosis), and unique pathologic patterns of brain metastases (namely, dural metastasis, leptomeningeal carcinomatosis, miliary metastasis, “intravascular carcinomatosis”, and tumor-to-tumor metastasis) with their clinical and radiological characteristics. We specifically address metastatic breast and non-small cell lung cancers which are the two most commonly encountered in daily practice, with emphasis on the molecular alterations related to therapy and their clinicopathologic significance.

Subependymoma is a rare subtype of benign ependymal neoplasm with distinct histological features. Anaplastic transformation has not yet been reported in this tumor to date. We present here a very unusual case of a 62‐year‐old woman with recurrent subependymoma of the fourth ventricle with multiple atypical histological features. Histologically, the resected recurrent tumor showed characteristic small cell clusters and nests of ependymal cells with an interspersed gliofibrillary matrix as seen in a classic subependymoma. In addition, there were very unusual histological features, including multiple areas of necrosis, microvascular proliferation, thrombosed blood vessels, and scattered mitotic figures. No coexisting ependymoma component of higher World Health Organization (WHO) grade was present. Immunohistochemically, MIB‐1 labeling index was high, with up to 15% in the highest areas. Review of this patient's initial tumor, which was resected 6 years prior to recurrence, demonstrated features of a typical classic subependymoma without atypical features or a secondary tumor component. Subependymomas are known to be low‐grade tumors and are usually cured if completely excised. The tumor presented here is unique in that several atypical pathological features were found in an otherwise typical subependymoma. Our case may represent anaplastic transformation of subependymoma, although no such examples have been reported to date.

Objectives: The etiology of pleural effusions (PEs) varies, and a percentage of PEs remains unexplained despite an intensive workup. One previous study documented a high prevalence of Epstein-Barr virus (EBV)–DNA in unselected and unexplained PEs. Our aim is to characterize the clinical and cytomorphologic features of EBV-associated PEs, which have not been described. Methods: A database search was performed for PEs with EBV-DNA identified in the fluid by real-time quantitative polymerase chain reaction. The corresponding fluid cytology and chemistry were reviewed, and the patients’ demographic data and clinical features were recorded. Results: A total of 20 cases of EBV-DNA–positive PE were found. All patients had a history of lung transplantation. Most of the PE EBV loads were relatively low. Cytologically, polymorphous lymphocytosis was present in more than 70% of PEs. Scattered lymphocytic mitosis and apoptosis were seen in some cases. Mesothelial cells varied in number, and some cases showed reactive atypia. The lymphocytes were predominantly T cells with the CD4/CD8 ratio varying from 10:1 to 3:20. Conclusions: EBV infection/reactivation can account for certain proportions of “idiopathic” PEs. Polymorphous lymphocytosis is the most common cytologic feature, but atypical features (in both lymphocytes and mesothelial cells) can be seen.

Although Epstein-Barr virus (EBV) infection has been known to be associated with a heterogeneous group of malignancies including Hodgkin lymphoma (HL), its association with smooth-muscle tumors (SMTs) has recently been described. Of these SMTs, a primary intracranial EBV-associated leiomyosarcoma (EBV-LMS) is extremely rare, and most of the reported cases were of immunocompromised and/or pediatric patients. A neurologically asymptomatic, previously healthy 27-year-old man was found to have a PET-positive brain lesion during a staging workup for his recently diagnosed HL. Subsequent MRI revealed a 2.6 × 4.0 × 3.3–cm inhomogeneously enhancing tumor with marked surrounding edema in the right anterior frontal lobe. He was serologically HIV negative. He underwent a right frontal lobectomy with gross-total resection of the tumor. Intraoperatively, the tumor had fairly discrete margins and appeared to arise from the anterior falx (that is, it was dural based). Microscopically, the tumor was composed of interlacing fascicles of spindle cells with brisk mitotic activity and multiple foci of necrosis. Immunohistochemically, the tumor cells were positive for caldesmon and smooth-muscle actin and negative for desmin, CD34, CD99, bcl-2, S100 protein, and GFAP. A Ki-67 labeling index was up to 30%. Epstein-Barr virus–encoded RNA in situ hybridization demonstrated strong diffuse positivity with more than 90% of tumor cells staining. Most of the Reed-Sternberg cells in HL were also labeled with Epstein-Barr virus–encoded RNA. This is the first case of a concurrent occurrence of rare intracranial EBV-LMS and HL in a seemingly “immunocompetent” adult patient (immunocompetence determined by routine laboratory data and clinical history). We should be aware of EBV-SMT as a differential diagnosis of dural-based spindle cell neoplasm in this setting given that patients with HL, even at presentation, exhibit a persistent defect in cellular immunity.

An atypical teratoid/rhabdoid tumor (AT/RT) is a highly malignant embryonal tumor most often occurring in the posterior fossa in children younger than 3 years of age. Adult cases of AT/RT are very rare, and 27 cases with a diagnosis of either AT/RT or (malignant) rhabdoid tumor have been reported to date. The authors report an adult case of an AT/RT occurring in the pineal region with molecular cytogenetic and immunohistochemical confirmation. A 33-year-old woman presented with a 2-month history of headache and blurred vision progressing to diplopia, and was admitted emergently due to deteriorating mental status. An MR image showed a heterogeneously enhancing mass involving the posterior third ventricle and pineal region with mild hydrocephalus. She underwent a subtotal resection of the tumor and was then treated with chemoradiation. Thirteen months after surgery, she was still alive with radiological evidence of recurrence/residual lesions. Histological sections showed epithelioid cellular sheets of rhabdoid tumor cells with scattered mitotic figures. Immunohistochemically, the tumor cells were diffusely and strongly positive for epithelial membrane antigen and vimentin, and showed focal expression of glial fibrillary acidic protein, pancytokeratin, and neurofilament protein. Loss of nuclear immunoreactivity for INI1 protein was observed. Fluorescence in situ hybridization analysis showed monosomy 22. Histologically, this tumor consisted exclusively of epithelioid tumor cells with rhabdoid features. The differential diagnoses include rhabdoid glioblastoma, metastatic carcinoma, and rhabdoid meningioma. Molecular testing to identify monosomy 22 or deletions of the chromosome 22q11 containing the INI1/hSNF5 gene and/or immunohistochemical staining with INI1 antibody is of great importance for the diagnosis of this tumor.

Hemangioblastomas (HBs) account for nearly a tenth of all posterior fossa neoplasms and can be the presenting finding in patients with von Hippel-Lindau (VHL) syndrome. HB must be differentiated from renal cell carcinoma (RCC), also seen in VHL, as the distinction between these lesions dictates the management of these patients. Currently inhibin A and RCC marker have been used in the diagnosis of HB and metastatic RCC, both with inconsistent results. Additional immunohistochemical markers including CD10, PAX-2, D2-40, and FLi-1 have been shown to have potential for the distinction of these two entities. Fifteen cerebellar HBs and 17 metastatic clear cell RCCs to the brain were selected for the study. All cases were immunostained with RCC marker, inhibin, CD10, PAX-2, D2-40, and Fli-1. The staining patterns were scored based on intensity and extent of tumor staining. In the differentiation of HB and metastatic RCC, D2-40 and RCC marker proved to be poor markers with less than 50% of HBs and RCCs, respectively, showing positive staining. PAX-2 and CD10 were superior to RCC marker in the diagnosis of metastatic RCC, with PAX-2 having better specificity. Fli-1 failed to stain tumor cells in both HBs and RCC. Inhibin A, in combination with PAX-2, showed to be the most useful markers to differentiate HB from metastatic RCC.

Immunohistochemistry (IHC) has become an important adjunct tool in diagnostic neuro-oncology practice enabling immunophenotypic characterization of tumor cells. There have been several recent publications regarding new IHC markers that are useful for diagnosis of brain tumors. To introduce the latest advances in IHC in this field, we review the features of novel IHC marker antibodies applicable to selected nonglial tumors in the nervous system, based on recently published reports and our own experiences. We discuss (1) aquaporin-1 and alpha-inhibin for hemangioblastoma, (2) beta-catenin for craniopharyngioma, (3) brachyury for chordoma, and (4) INI-1 for hereditary schwannomas. All the markers presented here are used primarily for supporting or confirming the histologic diagnosis, with the exception of (4), which may be of help in identification of inherited forms in schwannomas. As with other surgical pathology practices, the judicious use of a panel of IHC antibodies selected on the basis of the histologic findings is important for an accurate diagnosis of brain tumors. Of note is that IHC results should be always interpreted in the histopathologic context.