Dermatomal Microcycstic Lymphatic Malformation: A Case Report of an Unusual Presentation.

Background: Microcystic lymphatic malformation (MLM), previously termed lymphangioma circumscriptum, is a rare congenital lymphatic malformation typically presenting as grouped translucent or hemorrhagic vesicles resembling frog spawn, most often on the axilla, neck, shoulders, and proximal extremities. Dermatomal distribution is exceptionally rare. Case Presentation: A 17-year-old female presented with a long-standing, gradually enlarging lesion of grouped papules and vesicles along the left flank and lateral thigh, distributed in a linear dermatomal pattern (T10-T12) and sharply respecting the midline. Lesions were translucent, skin-colored, erythematous, and hemorrhagic, with a verrucous surface resembling frog spawn. Histopathology showed dilated papillary dermal lymphatic channels containing proteinaceous fluid and red blood cells, with hyperkeratosis, acanthosis, papillomatosis, and focal dermal fibrosis, confirming MLM. Surgical excision was recommended given the deep lymphatic involvement. Conclusion: This case illustrates a rare dermatomal presentation of MLM, likely reflecting somatic mosaicism of mesodermal lymphatic endothelium. Histopathological confirmation is essential to avoid misdiagnosis, and complete surgical excision remains the preferred treatment to minimize recurrence.