Facial infiltrating lipomatosis: a case report of longstanding craniofacial involvement in an adult and literature review

Facial infiltrating lipomatosis (FIL) is a rare craniofacial malformation characterized by diffuse infiltration of mature adipose tissue into adjacent soft tissues and skeletal structures and is currently classified within the PIK3CA-related overgrowth spectrum (PROS). Although FIL is usually recognized in childhood, adult presentations are infrequently reported. A literature review identified 12 previously reported cases in patients aged 30 years or older, emphasizing the rarity of adult diagnosis. This report describes a 56-year-old woman with a lower lip nodule and longstanding right-sided hemifacial asymmetry since childhood. Multimodal imaging demonstrated fatty infiltration of the masticatory muscles and temporomandibular joint (TMJ) osteohypertrophy. Histopathological examination revealed non-encapsulated mature adipose tissue without atypia. The diagnosis was established through clinicopathological correlation with imaging and immunohistochemical findings. Because of extensive involvement of the masticatory muscles and TMJ structures, conservative management was selected due to the potential functional morbidity associated with surgical resection. The patient accepted conservative management and remains under clinical and imaging follow-up. This case illustrates that FIL may remain unrecognized for decades and should be considered among the differential diagnoses of longstanding unilateral craniofacial overgrowth. Multimodal clinicopathological correlation is important for establishing the diagnosis and defining disease extent.