Intrasinusoidal bone marrow involvement is an infrequent histological pattern observed in a limited number of B and T cell lymphomas. Mantle cell lymphoma is a biologically and prognostically heterogeneous B cell lymphoma that frequently involves the bone marrow, with interstitial, nodular-paratrabecular, or diffuse patterns. Intrasinusoidal bone marrow involvement has been described only anecdotally in this lymphoma. Here, we describe the clinical, histopathological, and molecular features of four patients diagnosed with advanced-stage mantle cell lymphoma, showing intrasinusoidal bone marrow involvement, and other peculiar immunophenotypical features. As similar cases may represent a relevant issue in bone marrow diagnostic histopathology, we also reviewed the literature to discuss differential diagnoses of B and T cell lymphomas with intrasinusoidal bone marrow involvement.

Interfollicular Hodgkin lymphoma (IHL) has been rarely reported in the literature and is recognized by the WHO Classification as a morphologic pattern sometimes seen in mixed cellularity classic Hodgkin lymphoma (CHL). The changes may be subtle due to preservation of architecture. We report a case of a 9-year-old male with IHL showing preserved follicular architecture but with the presence of interfollicular infiltrates consisting of eosinophils, plasma cells, and Hodgkin-Reed-Sternberg (HRS) cells. Immunophenotyping confirmed the morphologic suspicion for IHL. A discussion and review of the literature are offered. We conclude that IHL is a variant that requires a high index of suspicion, as it may be easily missed due to the subtle morphologic features and preserved architecture seen in most cases. We further emphasize that unexplained interfollicular infiltrates of eosinophils may be clues that should prompt a search of HRS cells and consideration of immunohistochemical staining if needed.

Intravascular large B-cell lymphoma (IVLBCL) is a rare lymphoma that affects the brain, skin, and bone marrow. We describe the case of a 75-year-old man who was admitted to the hospital after 4 h of stomach aches. A thorough physical examination indicated stomach discomfort and skin discoloration. Laboratory tests revealed thrombocytopenia and elevated lactate dehydrogenase levels. A computed tomography scan of the abdomen revealed that the small intestine wall was thickened, edematous, and necrotic. The necrotic small bowel was surgically removed, revealing many little round, homogenous, and unusual cells in the mesenteric vein. In-situ hybridization revealed that these cells were positive for PAX5, CD20, CD79a, CD10, and BCL2, as well as Epstein-Barr virus-encoded small RNA. After 1 week of hospitalization without treatment, the patient was diagnosed with IVLBCL and died of multiple organ dysfunction syndrome. IVLBCL is a rare illness that affects the small intestine and possibly the gastrointestinal system. It has an insidious start, a fast development, and a dismal prognosis. Knowing its clinicopathologic traits helps in understanding the illness, making an early diagnosis, and preventing rapid worsening.

Fibroblastic reticulum cell tumor (FRCT) is a rare dendritic neoplasm arising from fibroblastic reticulum cells (FBRCs) and exhibiting peculiar cytokeratin expression. FRCTs usually involve the lymph nodes, although they can also be encountered in the spleen and soft tissues. FRCTs are composed of mildly atypical spindle or ovoid cells, arranged in loose whorls, which express almost invariably low-weight cytokeratins, smooth muscle actin, and CD68. An admixed lymphoplasmacytic infiltrate is also frequently present in solid organ sites. The clinical picture may vary from very indolent to aggressive disease exhibiting features of malignancy, such as cytological pleomorphism, necrosis, or high mitotic rate and metastatic potential. FRCT is a challenging diagnosis, due to its rarity and deceptive cytokeratin expression. Hereafter, we revise the most recent literature regarding such condition and report the case of an extremely indolent splenic FRCT, with no features of malignancy.

BACKGROUND: Gastrointestinal complications are not uncommon in patients of Acute Leukemia. Intussusception as a complication in leukemia, although described, is exceedingly rare. Also, it is usually seen after chemotherapy and not as a part of the native disease process. This case report aims to highlight such a rare association which warrants clinical and pathological attention.
METHODS: A 14 year old male presented with an acute abdomen. Initial routine investigations revealed a deranged blood picture. On further examination of bone marrow aspirate, biopsy and detailed immunohistochemical studies a diagnosis of B-Acute Lymphoblastic Leukemia (B-ALL) was made. Concurrent ultrasound of the abdomen to find a cause for severe abdominal pain revealed an Ileo-colic intussusception. The patient was started on steroids; however he succumbed to his illness after two days, before surgery could be attempted.
CONCLUSIONS: Rare presentations of relatively common diseases are a hurdle for timely and effective medical intervention. Although a rare condition in itself in leukemic patients, the occurrence of Intussusception in this particular patient, especially when no chemotherapy was initiated, is a very rare event. This case report was made to add to the relatively scarce literature available on this particular association. As it is a surgically treatable condition and since delay in diagnosis may lead to poorer prognosis, possibility of co-existence of ALL and intussusception should be borne in mind by all treating physicians and hematopathologists for effective patient care.

OBJECTIVE: Haemophagocytic lymphohistiocytosis (HLH) is divided into paediatric (primary) and adult (secondary) types. While paediatric-HLH has been extensively characterised, similar studies in adults are limited. This study aims to evaluate the significance of the HLH diagnostic criteria as well as other clinical parameters in adults with bone marrow evidence of haemophagocytosis.
METHODS: We conducted a 10-year retrospective search of the pathology archives of two institutions for cases with bone marrow haemophagocytosis. We included those cases that fulfilled the currently established HLH diagnostic criteria. For the 29 cases that met inclusion criteria, we assessed clinical features, co-morbidities, therapy and clinical outcome. The effect of 19 clinical variables on mortality outcomes was assessed using logistic and hazard regression analyses.
RESULTS: Of cases for which an aetiology could be identified, infectious diseases were the most common association (14 of 19, 74%). Fever and elevated ferritin were the most frequently available criteria used to establish HLH. The overall mortality rate was 61% despite HLH-specific therapy, which had been initiated in 48% of the cases. The remaining cases were treated with supportive therapy and antibiotics. The most statistically significant marker of mortality was an elevated absolute neutrophil count (ANC), a feature not typical of HLH.
CONCLUSIONS: Since elevated ANC correlates with poor outcomes in sepsis, and not HLH, we postulate that many of the patients fulfilling HLH diagnostic criteria in this study likely had sepsis/systemic inflammatory response syndrome rather than HLH. Our results highlight the need to define HLH diagnostic criteria specific to the adult population.

OBJECTIVE: To describe the radiologic and clinicopathologic features of extranodal Rosai-Dorfman disease (RDD) in our patient population.
METHODS: Via a data mining engine, we evaluated 13 cases of extranodal RDD in 10 patients treated at our institution from 2000 to 2014.
RESULTS: There was a marked female predominance (90%) in our series. The most common clinical presentation was a palpable, painless mass, which often simulated a neoplasm. Only two cases occurred in children. Multicentric and recurrent disease were uncommon. Histologically, all cases showed large histiocytes with emperipolesis in a mixed inflammatory background, with areas of dense, storiform collagen fibrosis. Positive S-100 and CD68 with negative CD1a in histiocytes are characteristic.
CONCLUSIONS: Extranodal RDD is rare and its manifestations varied. It may constitute a clinical and pathologic diagnostic challenge. Clinical suspicion and recognition of its histologic features are necessary for correct diagnosis and avoiding unnecessary treatment. Resection is curative in most cases.

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OBJECTIVE: B-lymphoblastic leukemia (B-ALL) with intrachromosomal amplification of chromosome 21 (iAMP21) is a relatively uncommon manifestation of acute leukemia and limited predominantly to the pediatric population. Case-specific information regarding flow cytometric, morphologic, and laboratory findings of this subtype of leukemia is currently lacking.
METHODS: We searched the databases of three large institutions for lymphoblastic leukemia with iAMP21 from 2005 through 2012 and analyzed the clinicopathologic features.
RESULTS: We identified 17 cases with five or more RUNX1 signals on interphase nuclei, 14 of which were consistent with the Children\'s Oncology Group (COG) definition for iAMP21—namely, the presence of three or more RUNX1 signals on one marker chromosome. These cases showed a statistically significant lower peripheral WBC count and older age at diagnosis compared with all pediatric cases of B-ALL. We also identified three cases with increased RUNX1 signals scattered on multiple marker chromosomes that did not meet the COG definition of iAMP21 but showed similar 21q instability and older age at presentation.
CONCLUSIONS: Our findings not only demonstrate that B-ALL with iAMP21 is truly a distinct clinicopathologic entity but also suggest that a subset of cases of B-ALL with iAMP21 can show variable cytogenetic features.