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Notes: Most follicular lymphomas can be readily diagnosed on morphological grounds by finding closely packed pale-staining follicles partitioned by scanty dark-staining inter-follicular tissue. We describe two cases of an unusual ‘reverse’ variant of follicular lymphoma in which the nodules have dark-staining centres and pale-staining cuffs due to concentration of centroblasts at the periphery of the neoplastic follicles. Recognition of this unusual pattern of follicular lymphoma is important, to avoid confusion with progressive transformation of germinal centres or nodular lymphocyte predominance Hodgkin's disease.

Notes: Aims:  Pulmonary sclerosing haemangioma is a rare benign tumour with a characteristic variegated histological pattern. In this retrospective study we aimed to identify features that can aid in making a correct diagnosis and avoiding potential pitfalls at the time of intra-operative frozen section.Methods and results:  Twenty cases of pulmonary sclerosing haemangioma with intra-operative frozen section were reviewed. The four major histological patterns (solid, sclerotic, papillary and haemorrhagic) were found in various combinations in the frozen sections. In 17 cases, three or more patterns were present. There could be focal areas mimicking epithelioid haemangioendothelioma or carcinoid tumour. Intra-operative imprint/scrape cytology served as a helpful adjunct in confirming the cytological blandness, although occasional atypical cells could be present. An intra-operative frozen section diagnosis of ‘sclerosing haemangioma’ or ‘benign tumour’ was given in 14 cases; the diagnosis was deferred in six cases. Retrospective analysis of the deferred cases showed that a definitive intra-operative diagnosis could have been made in three, because three or more major histological patterns were present. One case showed a pure papillary pattern at frozen section, mimicking the appearance of papillary adenocarcinoma (primary or secondary), bronchioloalveolar carcinoma, epithelioid mesothelioma or papillary adenoma; two tumours from a patient with multicentric disease showed widespread significant cytological atypia in the tumours raising a serious consideration of malignancy.Conclusion:  A diagnosis of pulmonary sclerosing haemangioma can be made at intra-operative frozen sections in most cases based on the tumour circumscription and variegated histological patterns. When only a single histological pattern is identified or when there is significant cytological atypia, distinction from other tumours can be problematic, and the diagnosis is best deferred.

Notes: Tumours of histiocytes and accessory dendritic cells: an immunohistochemical approach to classification from the International Lymphoma Study Group based on 61 cases Neoplasms of histiocytes and dendritic cells are rare, and their phenotypic and biological definition is incomplete. Seeking to identify antigens detectable in paraffin-embedded sections that might allow a more complete, rational immunophenotypic classification of histiocytic/dendritic cell neoplasms, the International Lymphoma Study Group (ILSG) stained 61 tumours of suspected histiocytic/dendritic cell type with a panel of 15 antibodies including those reactive with histiocytes (CD68, lysozyme (LYS)), Langerhans cells (CD1a), follicular dendritic cells (FDC: CD21, CD35) and S100 protein. This analysis revealed that 57 cases (93%) fit into four major immunophenotypic groups (one histiocytic and three dendritic cell types) utilizing six markers: CD68, LYS, CD1a, S100, CD21, and CD35. The four (7%) unclassified cases were further classifiable into the above four groups using additional morphological and ultrastructural features. The four groups then included: (i) histiocytic sarcoma (n=18) with the following phenotype: CD68 (100%), LYS (94%), CD1a (0%), S100 (33%), CD21/35 (0%). The median age was 46 years. Presentation was predominantly extranodal (72%) with high mortality (58% dead of disease (DOD)). Three had systemic involvement consistent with `malignant histiocytosis'; (ii) Langerhans cell tumour (LCT) (n=26) which expressed: CD68 (96%), LYS (42%), CD1a (100%), S100 (100%), CD21/35 (0%). There were two morphological variants: cytologically typical (n=17) designated LCT; and cytologically malignant (n=9) designated Langerhans cell sarcoma (LCS). The LCS were often not easily recognized morphologically as LC-derived, but were diagnosed based on CD1a staining. LCT and LCS differed in median age (33 versus 41 years), male:female ratio (3.7:1 versus 1:2), and death rate (31% versus 50% DOD). Four LCT patients had systemic involvement typical of Letterer–Siwe disease; (iii) follicular dendritic cell tumour/sarcoma (FDCT) (n=13) which expressed: CD68 (54%), LYS (8%), CD1a (0%), S100 (16%), FDC markers CD21/35 (100%), EMA (40%). These patients were adults (median age 65 years) with predominantly localized nodal disease (75%) and low mortality (9% DOD); (iv) interdigitating dendritic cell tumour/sarcoma (IDCT) (n=4) which expressed: CD68 (50%), LYS (25%), CD1a (0%), S100 (100%), CD21/35 (0%). The patients were adults (median 71 years) with localized nodal disease (75%) without mortality (0% DOD). In conclusion, definitive immunophenotypic classification of histiocytic and accessory cell neoplasms into four categories was possible in 93% of the cases using six antigens detected in paraffin-embedded sections. Exceptional cases (7%) were resolvable when added morphological and ultrastructural features were considered. We propose a classification combining immunophenotype and morphology with five categories, including Langerhans cell sarcoma. This simplified scheme is practical for everyday diagnostic use and should provide a framework for additional investigation of these unusual neoplasms.

Notes: Capsular intravascular endothelial hyperplasia: a peculiar form of vasoproliferative lesion associated with thyroid carcinoma Aims: Florid vasoproliferative processes are uncommon in the thyroid gland. We report three cases of an unusual vasoproliferation involving the capsular blood vessels of thyroid carcinoma. Methods and results: The histological diagnoses of the three cases were made on conventional histological sections. Two cases were minimally invasive follicular carcinomas and one case was an encapsulated variant of papillary carcinoma. Some blood vessels in the tumour fibrous capsule were filled with spindly cellular proliferations forming irregular vascular clefts and papillae. Immunohistochemical studies for CD31, CD34 and muscle-specific actin confirmed that the spindly cells were mostly endothelial cells variably supported by pericytes. Conclusion: This peculiar intravascular endothelial hyperplasia by itself should not be mistaken for vascular invasion by tumour, but evidence of malignancy must be diligently sought by extensive sampling because the lesion has thus far been consistently associated with malignant thyroid neoplasms.

Notes: This report describes two cases of alveolar rhabdomyosarcoma of the nasal cavity with unusual histological appearances mimicking clear cell carcinoma. The closely packed tumour cells were polygonal and arranged in sheets and packets. They had an appreciable amount of clear cytoplasm due to accumulation of glycogen. The diagnosis of rhabdomyosarcoma was confirmed by positive staining for desmin and myoglobin. Rhabdomyosarcoma should be included in the differential diagnosis of nasal clear cell tumours, particularly in young adults. A correct diagnosis is important, because chemotherapy is indicated even for apparently localized disease.

Notes: Penicillium marneffei is a rare human pathogen that often causes problems in clinical and histological diagnosis. A patient who presented with autoimmune haemolytic anaemia and hepatosplenomegaly, and was subsequently found to be suffering from disseminated Penicillium marneffei infection, is reported. The liver biopsy showed epithelioid cell granulomas only, and tuberculosis was initially considered the most likely diagnosis. The correct diagnosis became evident in a subsequent colonic biopsy, which showed extensive infiltration by penicillium-laden macrophages.

Notes: This report describes 16 cases of the recently recognized anaplastic large cell Ki-1 lymphoma. The disease showed a male:female ratio of 2.2:1 and a bimodal age distribution with peaks in the third and eighth decades. The clinical presentation was highly variable, with lymph node, skin, bone and gastrointestinal tract being the most commonly affected sites. The lymph nodes usually showed subtotal or sinusoidal involvement, and parenchymal fibrosis was common. The large neoplastic cells were almost invariably admixed with many reactive small lymphocytes, histiocytes and/or neutrophils. Two cytological types could be delineated: type I (pale cell, four cases) consisted of large polygonal cells with distinct pink-staining cell membrane and pale cytoplasm and pleomorphic nuclei showing marked chromatin clearing; and type II (basophilic cell, 12 cases) consisted of round or oval cells with basophilic cytoplasm and/or paranuclear pale hof, pleomorphic nuclei often reniform or lobulated and with frequent multinucleated wreath-like and Reed-Sternberg-like cells. Immunohistochemical studies showed that nine cases (56.3%) exhibited a T-cell phenotype, three cases (18.8%) each exhibited a B-cell or null-cell phenotype, while one case exhibited both T- and B-cell markers. Cutaneous involvement at presentation was associated with a favourable outcome, and spontaneous regression was common. For patients with non-cutaneous presentation, the prognosis was relatively good for young patients treated with aggressive chemotherapy, but was grave for old patients.