Angiomyoid proliferative lesion: an unusual stroma-rich variant of Castleman's disease of hyaline-vascular type.

The stroma-rich variant of Castleman's disease of hyaline-vascular type (CDHV) is a newly identified entity that shows overgrowth of a variety of stromal cells. Six CDHV patients showed proliferation of vasculature and actin-positive myoid cells in the expanded interfollicular (IF) area. There were three women and three men, and the median age was 29.5 years. Of the six lesions, four were located in the retroperitoneum, one in the neck, and one in the mediastinum. All patients were asymptomatic. Microscopically, the degree of widening of the IF area varied from slight overgrowth of the IF area (approximately 55% of the lymph node area) to vague nodularity and finally to the formation of prominent nodules. In the nodular lesions, lymph follicles were compressed and attenuated. In the IF area, there were numerous vessels and proliferation of spindle cells that possessed blunt nuclei. The long, slender, dendritic cytoplasms of the spindle cells were stained by alpha smooth muscle actin. The spindle cells were negative for desmin, CD34, factor VIII-related antigen, S-100, CD21, and CD68. No patient has had recurrence after simple excision. We maintain that these angiomyoid proliferative lesions in CDHV are of a hyperplastic nature. This condition encompasses proliferation of small vessels and myoid cells. Its characteristics include an asymptomatic, solitary nodule that predominantly develops in the retroperitoneum.