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Radiation lung injury typically occurs after treatment for malignancies, including lung, esophagus, breast, and hematopoietic malignancies. The risk has decreased with development of radiation treatment with lower doses to lung fields via intensity modulated and stereotactic procedures. The risk is still substantial in some settings, such as total body radiation in patients with stem cell transplants or stem cell transplants in patients with recurrent Hodgkin lymphoma. Histologically, radiation injury progresses from acute alveolar injury (diffuse alveolar damage) through a fibrotic phase resembling nonspecific interstitial pneumonia. The histologic features are nonspecific, but atypical pneumocytes are especially enlarged and bizarre in the acute and subacute phases of radiation-induced lung injury. We present a case of radiation fibrosis requiring transplant in a patient with relapsing mediastinal Hodgkin lymphoma requiring stem cell transplant and repeat mediastinal radiation.

Early renal allograft dysfunction is often associated with acute rejection (cellular or antibody mediated) or graft injury due to ischemia or surgical complications. Correlation of clinical, laboratory, and imaging studies are crucial in the assessment of patients with early graft dysfunction. Renal allograft biopsy is often necessary for diagnosis and to guide definitive therapy. We present a case of early graft dysfunction with an unusual clinical presentation and histologic picture. A high index of clinical suspicion along with electron microscopic studies led to the diagnosis.

Systemic Epstein-Barr virus (EBV)–positive T-cell lymphoproliferative disease of childhood is a rare, aggressive T-cell malignancy recently recognized in the 2008 World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues. This disease classically arises in the context of primary acute or chronic active EBV infection, and it is characterized by a clonal proliferation of EBV-infected T cells with an activated cytotoxic phenotype. Most patients have a fulminant clinical course. The clinical and pathologic features of the disease overlap with other conditions, such as infectious mononucleosis, chronic active EBV infection, hemophagocytic lymphohistiocytosis, and natural killer cell malignancies. Here we report a case of systemic EBV+ T-cell lymphoproliferative disease of childhood, and the key features and diagnostic pitfalls of this entity are discussed.

Sclerosing hemangioma of lung is an unusual neoplasm with distinctive morphological features. Although its histogenesis has been debated for decades, the current concept is that this is a tumor of cells with features most closely resembling type II pneumocytes. The tumor has 2 separate cellular components (surface cells and round cells) and 4 different growth patterns (solid, papillary, sclerotic, and hemorrhagic), which may be present in various degrees from one tumor to another. Both surface and round cells stain positive for TTF-1 and epithelial membrane antigen, whereas the surface cells stain strongly positive for cytokeratins and for surfactant proteins A and B. Round cells generally stain negative for cytokeratins and surfactant proteins. Ultrastructurally, the surface cells have features of type II pneumocytes with well-formed lamellar bodies, whereas the round cells are more primitive and contain dense core granules and microtubules. Despite the name of the tumor, vascular differentiation is not observed. Sclerosing hemangioma typically presents as a unilateral pulmonary nodule, but multiple and bilateral examples have been reported. Although this tumor typically behaves in a benign fashion with long-term survival expected after surgical resection, cases with lymph node metastases and more aggressive clinical behavior have been reported. This tumor has the potential for confusion with other more common and aggressive lung neoplasms, especially in cytological specimens. We report herein a case of sclerosing hemangioma of the lung with lymph node metastasis and review the literature on this unusual neoplasm.

Aneurysmal bone cyst (ABC) is a primary bone tumor that predominantly affects individuals in the first 2 decades of life. Imaging studies reveal an osteolytic, eccentric, and multicystic lesion. The neoplasm usually behaves in a benign fashion but may recur locally. Intralesional curettage is the treatment of choice, but surgical resection or other therapeutic approaches have been occasionally used. Aneurysmal bone cyst is characterized by the chromosomal translocation t(16;17)(q22;p13), which results in the fusion of the promoter region of the osteoblast cadherin 11 (CDH11) to the entire coding sequence of the ubiquitin protease USP6 in a classic promoter swapping mechanism. The fusion leads to USP6 transcriptional up-regulation and protein overexpression. Several alternate USP6 fusion genes have also been described, and more recent studies have shown that USP6 contributes to the pathogenesis of ABC via (1) activation of metalloproteases that promote osteolysis and matrix degradation and (2) inhibition of proteins involved in osteoblastic maturation. These new discoveries are enhancing our understanding of ABC biology and may lead to the development of novel therapeutic approaches for this tumor.

JC virus-associated progressive multifocal leukoencephalopathy (PML) continues to be an important cause of opportunistic infections in patients infected with human immunodeficiency virus (HIV). Here, we report a case of a 25-year-old man with a 2-year history of untreated HIV infection who presented with left hand weakness. After the initiation of highly active retroviral therapy, his viral load decreased, but his left-sided neurologic symptoms worsened. Findings from magnetic resonance imaging were consistent with PML, but no JC virus was detected in the central nervous system. The patient underwent brain biopsy, which revealed JC virus infection and changes associated with PML. This case illustrates the histopathologic findings in PML-immune reconstitution inflammatory syndrome, the phenomenon of paradoxical worsening of PML after initiation of HIV antiretroviral therapy, and highlights the limitations of JC virus detection in the cerebrospinal fluid for diagnosis.

Abstract The pathogenesis of injury to the developing brain encompasses low oxygen tension and decreased perfusion, often termed hypoxia-ischemia. Factors playing key roles in this setting include (1) inherent vulnerability of immature cells to conditions such as oxidative stress, cytokines, and excitotoxicity; (2) imperfect autoregulation of cerebral blood flow in the face of fluctuations in systemic perfusion pressure, especially in prematurity; (3) presence of blood products in direct contact with developing brain regions, such as the germinal matrix and cerebellum; (4) frequent co-occurrence of other serious illnesses, such as lung disease in the premature infant, or congenital heart disease in the term infant; and (5) significant antenatal conditions, for example, maternal pre-eclampsia with chronic placental hypoperfusion, or acute chorioamnionitis precipitating preterm delivery. The totality of neuropathology experienced by an infant is a summation over time of all of the above circumstances, which may be singular, intermittent, or continuous, or, most likely, a combination thereof. This article will attempt to shed light on the spectrum of injury seen in the perinatal brain and will comprise lesions encountered in the stillborn, the premature, and the term infant through the presentation of 4 illustrative case studies. These include a term stillbirth with diffuse white matter gliosis and selective neuronal vulnerability (pontosubicular necrosis); a 3-week-old premature infant with periventricular leukomalacia and thalamic/basal ganglionic injury; a premature infant with germinal matrix hemorrhage, complicated by periventricular hemorrhagic infarction; and a term infant with congenital heart disease requiring extracorporeal membrane oxygenation therapy, and global hypoxic-ischemic encephalopathy.

Mucoepidermoid carcinoma (MEC) is the most common salivary gland malignancy. Prototypically defined by an admixture of mucinous, epidermoid, and intermediate cells, MEC can have a myriad of cytologic variations and growth patterns ranging from cystic to solid that occasionally make this tumor difficult to grade or even diagnose. Although there is no other salivary gland tumor for which grading is as prognostically and therapeutically relevant, the ideal method for grading these tumors has been debated since their initial detailed description in 1945. Currently, 2 commonly used point-based scoring systems are those of Armed Forces Institute of Pathology and Brandwein, both of which consider a variety of cytomorphologic parameters, while assigning different weights to these. Recently, the t(11;19)(q21;p13) translocation resulting in MAML2 gene rearrangement has been identified in a majority of MEC regardless of the grade and has been suggested as an additional marker of favorable prognosis. MAML2 gene rearrangements are readily detected by fluorescence in situ hybridization and are also considered specific for MEC and thus a potential useful confirmatory diagnostic test if positive. The differential diagnosis for MEC varies depending on histologic grade and variant morphology. Biopsy specimens of minor salivary gland tumors pose unique diagnostic challenges, even beyond limited specimen size.