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Rhabdomyoblasts masquerading as histiocytes: A diagnostic pitfall

A 74 year old female from Mexico presented to the emergency department complaining of fever and foul smelling vaginal discharge. On examination, patient was febrile and a pelvic examination revealed an enlarged distended uterus. Ultrasonography identified a large uterine mass. Biopsy report of the mass was consistent with endometrial cancer. The patient underwent a total abdominal hysterectomy with bilateral salpingo-oophorectomy and pelvic lymph node dissection. The gross specimen showed a 10 cm polypoid mass arising from the uterine cavity. The histologic sections showed an extensive sarcomatous component comprised of sheets of cells with eccentrically placed nucleus, prominent single nucleolus and abundant eosinophilic cytoplasm with occasional cross striations (Figure 1(A)–(C)). Malignant glands were identified within the rhabdomyosarcomatous stroma. A diagnosis of carcinosarcoma/malignant müllerian mixed tumor with heterologous elements (rhabdomyosarcomatous elements comprising 90% of the tumor) was rendered. The pelvic lymph nodes and the pelvic wash were negative for metastases. A subsequent chest Computed axial tomography (CAT) scan showed innumerable bilateral multiple small nodules in the lung with associated hilar lymphadenopathy. Fine needle aspiration of the enlarged hilar lymph nodes was performed. Diff-Quik and pap smears showed abundant histiocytes with black anthracotic pigment and intermixed small and large lymphocytes (Figure 2(A)–(D)). A second population of predominantly scattered single large unpigmented cells with rare loose clusters was noted. The unpigmented cells had moderate amounts of dense cytoplasm with eccentric nuclei and prominent single large nucleoli. A proportion of these cells were “stripped” with “naked” nuclei only. No obvious glandular differentiation was identified on cytologic examination. Hematoxylin and eosin stained cell block sections showed a rare cluster of unpigmented cells with eccentrically placed nuclei and abundant eosinophilic cytoplasm (Figure 3 (A)). In light of the patient's history immunostains were performed. Immunostain for desmin highlighted the rhabdomyosarcoma cells while CD68 highlighted the histiocytes (Figure 3(B),(C)). The findings