Delayed Evolution of Neurofibromatosis Type 1 in a Child With an Isolated Cervical Plexiform Neurofibroma Initially Mimicking Cystic Lymphangioma.

We report the case of an 11-year-old female who presented with a progressively enlarging cystic neck swelling. CT demonstrated a multiloculated cystic lesion involving the right cervical soft tissue planes, suggestive of a cystic lymphangioma. There was no significant family history or clinical evidence of neurofibromatosis type 1 (NF1) at presentation. Surgical excision was performed, and histopathological examination with S100 immunohistochemistry confirmed the diagnosis of plexiform neurofibroma. At the one-year follow-up, the patient developed multiple café-au-lait macules and Lisch nodules of the iris, fulfilling the diagnostic criteria for NF1. The delayed appearance of these characteristic features established the diagnosis of evolving sporadic NF1. This case highlights that an isolated plexiform neurofibroma may be the initial manifestation of NF1 and can clinically and radiologically mimic other cervical soft tissue lesions. Careful long-term clinical, dermatological, and ophthalmological follow-up is essential for the timely recognition of additional diagnostic features and appropriate surveillance.