Two splenic lesions in need of clarification: hamartoma and inflammatory pseudotumor.

This short review is dedicated to a precise pathologic characterization of 2 uncommon and poorly defined lesions of the spleen and to their distinction from histologically similar processes. Splenic hamartoma represents an abnormally formed red pulp and is characterized by the presence of sinus-like structures lined by CD8(+) endothelia. The great variety of its morphologic appearances may result from the preponderant growth of one or another of the several components of the red pulp, ie, CD34(+) capillaries, myoid cells and macrophages. Therefore, it is proposed that "cord capillary hemangioma," myoid angio-endothelioma, and histiocyte-rich tumors are part of the spectrum of splenic hamartoma. Inflammatory pseudotumor (IPT) of the spleen is a reactive lesion, probably of multiple etiologies, characterized by a mixture of inflammatory cells and a minor, disorganized component of spindle cells. The latter include fibroblasts, SMA(+) myofibroblasts, and CD68(+) spindled histiocytes, establishing a close similarity with the IPT of the lymph node. This benign process needs to be distinguished from 2 others that have a predominant spindle cell component arranged in parallel bundles: the IPT-like follicular dendritic cell tumor, which is consistently associated with Epstein-Barr Virus; and the inflammatory myofibroblastic tumor, also often Epstein-Barr Virus-related and similar to those of the soft tissues, lung and other organs. These 2 lesions are neoplastic and therefore have a potentially worse prognosis than IPT.