Histiocytic sarcoma of the spleen: case report of asymptomatic onset of thrombocytopenia and complex imaging features.

Histiocytic sarcoma of the spleen, in which the malignant cells display morphologic and immunophenotypic features similar to those of mature tissue histiocytes, is a rare but potentially lethal condition that can remain asymptomatic or only mildly symptomatic for a long period of time. We studied a case of histiocytic sarcoma of the spleen in an 82-year-old woman with prolonged chronic thrombocytopenia that was non-responsive to steroid therapy. Ultrasonography, computed tomography, and magnetic resonance imaging showed a characteristically enlarged spleen and liver. Palliative irradiation therapy was clinically effective; however, disease progression proved lethal. Autopsy revealed the proliferation of tumor cells within the splenic sinus and the liver sinusoids, which displayed extreme hemophagocytosis and strong expression of the histiocytic markers CD68 (KP1 and PG-M1) and CD163. The postmortem diagnosis showed histiocytic sarcoma of the spleen with liver infiltration. This and previous reports indicate that early detection (facilitated by imaging and clinical features) and management may improve patient prognosis and survival. Histiocytic sarcoma of the spleen should be considered as a differential diagnosis in therapeutically unresponsive patients with chronic thrombocytopenia.