Histogenesis of adenomatoid tumour associated to pseudofibromatous periorchitis in an infant with hydrocele.

An 18-month-old infant with recurrent congenital hydrocele presented with a mass in the caput epididymis. The tumour and several fragments of the tunica vaginalis were removed and studied by light and electron microscopy. The tumour showed the characteristic histological pattern of an adenomatoid tumour of mesothelial origin. The histological appearance of the tunica vaginalis was not uniform; some areas resembled the adenomatoid tumour to the epididymis, others exhibited histological and ultrastructural features of a haemangioma, whilst elsewhere, the two patterns were intermingled. Finally, areas of pseudofibromatous periorchitis with vascular proliferation and slit-like structures lined by mesothelial cells were recognized. These features suggest that the adenomatoid tumour originated from a localized reactive process with inflammation and vascular proliferation enclosing occasional slit-like structures originating from the mesothelial lining of the tunica vaginalis. Subsequent regression of vascular proliferation and inflammatory infiltration and continued mesothelial proliferation would give rise to the typical mesothelial pattern of adenomatoid tumour.