Rhabdomyosarcoma round cell

The small round cell tumors of soft tissue (Fig. 4.9 see Table 4.4) compose a heterogeneous group of neoplasms that predominate in childhood and adolescence and share similar morphologic features. Rhabdomyosarcoma, PNET/ES, and lymphoma/leukemia are the prototypic members of this group. Another entity that may be confused with PNET is the intra-abdominal desmoplastic small round cell tumor. 

FIGURE 4.10 The solid form of primitive embryonal or alveolar rhabdomyosarcoma represents a prototypical small round cell malignancy for which several adjunctive studies are necessary. 

The extent of staining with myogenin is also helpful in subclassification, because the alveolar variant of rhabdomyosarcoma usually shows extensive labeling in nearly all neoplastic cells, whereas E-RMS shows more heterogeneous reactivity. Other small round cell tumors lack those determinants, with the notable exception of intra-abdominal desmoplastic small round cell tumors, which are usually positive for desmin, but not for myogenin. 

Many of the tumors of the nasal cavity and paranasal sinuses fall under the category of round cell neoplasms. Among these are olfactory neuroblastoma, sinonasal undifferentiated carcinoma, malignant melanoma, neuroendocrine carcinoma-small cell neuroendocrine carcinoma, malignant lymphoma, extramedullary plasmacytoma, invasive-ectopic pituitary adenoma, rhabdomyosarcoma, and Ewing s sarcoma (ES)-peripheral neuroectodermal tumor (ES/ PNET). But there is also a host of other epithelial lesions that are unique to the sinonasal tract. 

T-cell lymphoma, ALCL, AML, GIST, breast metaplastic carcinoma, ovarian sex cord stromal tumors, synovial sarcoma, Merkel cell carcinoma, endocrine and neuroendocrine tumors, desmoplastic small round cell tumor, melanoma, nephroblastoma, ependymoma, mesenchymal chondrosarcoma, extrarenal malignant rhabdoid tumor, rhabdomyosarcoma, meningeal... 

Rhabdomyosarcoma is a mesenchymal tumour of grey colour with partially cystic growth. (12) It mainly occurs during childhood. (277) The tumour cells appear small, round or spindle-like, hyperchromatic, occasionally with eosinophilic cytoplasm. (279) They show various stages of differentiation of embryonal skeletal muscle cells. This tumour originates from peribiliary located muscu-... 

Neuroblastomas are small, round, blue cell tumors that may arise in the adrenal gland and a variety of extra-adrenal sites. The differential diagnosis is wide and includes rhabdomyosarcoma, Ewing s sarcoma-primitive neuroectodermal tumor (ES-PNET), medulloblastoma, small cell osteosarcoma, lymphoblastic lymphoma, blastematous Wilms tumor, and small cell desmoplastic tumor. Numerous markers have been used for the diagnosis of neuroblastomas including NE markers, cytoskeletal proteins, catecholamine-synthesizing enzymes, and neuroblastoma-"specific antibodies (Eig. 

FIGURE 17.4 Embryonal rhabdomyosarcoma consists of small, round, polygonal, and elongated tumor cells with variable amounts of eosinophilic cytoplasm and hyperchromatic nuclei (hematoxylin-eosin, x200). 

FIGURE 17.5 Alveolar rhabdomyosarcoma displays fibrovascular septa lined by small, round tumor cells surrounding spaces with dispersed individual tumor cells (hematoxylin-eosin, x200). 

Carpentieri DF, Nichols K, Chou PM, et al. The expression of WTl in the differentiation of rhabdomyosarcoma from other pediatric small round blue cell tumors. Mod Pathol. 2002 15 1080-1086. 

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