Occult metastasis of rhabdomyosarcoma to lymph node with sinus pattern

Light microscopy of sections from the paraaortic and pelvic lymph nodes of a patient revealed micrometastases with sinus pattern. The diagnosis of metastatic rhabdomyosarcoma was confirmed ultrastructurally by demonstration of actin filaments and Z bands. To our knowledge occult metastases of rhabdomyosarcoma with purely sinus pattern have not been reported previously and diagnosis might be difficult to establish clinically or pathologically. However, recognition of the lymph node involvement changes the clinical staging and therapeutic regimen of this disease. Therefore, rhabdomyosarcoma should be included in the differential diagnosis of lymphadenopathies with sinus pattern. The disorders causing sinus pattern in lymph nodes are briefly reviewed.