Occipital Extracranial Dermoid Cyst in a Neonate With Cardiofaciocutaneous Syndrome Type 4 (CFC4): A Case Report.

Dermoid cysts are congenital inclusion lesions that arise from ectodermal entrapment along embryonic fusion lines; occipital extracranial involvement is particularly uncommon. Cardiofaciocutaneous syndrome type 4 (CFC4), a RASopathy caused by pathogenic variants in MAP2K2, presents with characteristic dermatologic, craniofacial, and multisystem findings. We report an occipital extracranial dermoid cyst in a neonate with CFC4, proposing a possible developmental association between these two rare entities. A 16-day-old female infant, born preterm at 28 weeks, presented with multiple firm, skin-colored nodules on the occipital scalp. Physical examination revealed three discrete nodules with overlying alopecia and variable fixation to deeper structures. The initial differential diagnosis included dermoid cyst, epidermoid cyst, osteoma cutis, and calcinosis cutis. Neuroimaging demonstrated well-defined extracranial soft tissue masses without intracranial extension, supporting the diagnosis of an occipital dermoid cyst. Genetic testing was pursued due to dysmorphic features and confirmed a pathogenic MAP2K2 mutation, consistent with CFC4. In the absence of mass effect, ulceration, or neurologic compromise, conservative management and close clinical follow-up were recommended. Serial evaluations showed stability without progression. This case highlights an atypical occipital extracranial dermoid cyst in the setting of CFC4 and emphasizes two practical points: first, atypical scalp lesions in neonates warrant early imaging to exclude intracranial connection; second, syndromic evaluation (including molecular testing) should be considered when such lesions coexist with dysmorphic or ectodermal findings. Further observation and accumulation of similar cases are needed to explore a potential link between RASopathies and abnormal ectodermal/developmental fusion along the posterior scalp.