Epithelial and mesenchymal hamartomatous changes in a mature port-wine stain: Morphologic evidence for a multiple germ layer field defect.

The port-wine stain (PWS) is a congenital cutaneous venulocapillary malformation of unknown pathogenesis. Many patients with facial PWS develop thickening with cobblestoning and nodularity during adult life. The histologic correlates of this maturational change are poorly documented and its mechanisms remain unclear. In this case study we present new histologic observations that may elucidate this phenomenon. An extensive PWS on the face of a 75-year-old man exhibited gross thickening with cobblestoning and nodularity. Histologic examination revealed not only the expected vascular abnormalities, but also a number of widely distributed epithelial, neural, and mesenchymal hamartomatous changes. Epithelial changes included epidermal nevus, sebaceous trichofolliculoma, and basaloid follicular hamartoma. Changes of connective tissue nevus, smooth-muscle hamartoma, neural hamartoma, and subcuticular hamartoma were also noted. The complex hamartomatous changes observed in the PWS of this patient involved multiple germ lines and were distributed in a widespread pattern. These changes not only offer an explanation for the skin thickening and nodularity of this patient, but also suggest a genetically determined, multilineage developmental field defect in the pathogenesis of this lesion. Further studies of other patients are necessary to understand the full implications of these findings in the late stage of PWS.