Purpose or Case Report:
Subcutaneous fat necrosis of the newborn (SCFN) is an infrequent, self-limiting panniculitis observed in neonates. We report an unusual presentation of SCFN in a premature infant who developed a progressively enlarging mass in the supraclavicular region. Lesions commonly develop on the shoulders, back, buttocks, thighs, and cheeks.
The patient was a male infant born via emergency cesarean delivery at 30 weeks and 6 days gestation due to fetal distress. Maternal history was significant for diabetes. His postnatal course was complicated by hypoglycemia, episodes of apnea associated with hypoxia, and hypotension.
Physical examination revealed a firm, non-tender, subcutaneous mass without overlying skin changes in the left supraclavicular area. Ultrasonography demonstrated ill-defined thickening of the subcutaneous fat with heterogeneous echogenicity and internal blood flow. MRI showed reduced T1 signal intensity lower than that of normal fat and increased signal on T2 and fat-suppressed T2 sequences, indicating abnormal subcutaneous fat.
The differential diagnosis included SCFN, infantile myofibromatosis, embryonal rhabdomyosarcoma, hemangioma, and neurofibroma. Embryonal rhabdomyosarcoma is the most prevalent tumor affecting young children. Unlike subcutaneous fat necrosis, however, rhabdomyosarcoma typically arises after the first few months of life. It usually presents as a solitary, rapidly growing, firm mass involving striated muscle. Infantile myofibromatosis commonly involves multiple sites, including the bone, lungs, heart, and gastrointestinal tract. Given the infant’s prematurity and clinical history of perinatal hypoxia, metabolic derangements, and maternal diabetes, SCFN was considered the most likely diagnosis.
While SCFN resolves spontaneously, the most significant potential complication is hypercalcemia, which occurs in approximately 28% of cases. Additionally, renal ultrasound should be performed to assess nephrocalcinosis and nephrolithiasis.
In summary, subcutaneous fat necrosis may be present in premature infants with relevant perinatal risk factors. Its clinical and radiologic features can mimic neoplastic or infectious conditions. It is essential for radiologists to recognize the clinical and imaging characteristics of this rare condition to enable timely diagnosis and avoid unwarranted surgical intervention.
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