Radiological Case of the Month

Figure 1. Photograph of the back showing the large, sharply circumscribed lesion.

Figure 2. Magnetic resonance imaging scan of the thorax. A, Sagittal T2-weighted image shows swelling of the subcutaneous fat on the back with the presence of hyperintense streaks. B, Sagittal T1-weighted image shows a hypointense signal with homogeneous poor enhancement after a contrast injection (C).

Subcutaneous fat necrosis (SFN) in the newborn is a rare, transient inflammatory disorder of adipose tissue attributed to perinatal stress such as birth trauma, asphyxia, meconium aspiration, or exposure to cold.^1-3 Prolonged hypothermic cardiac surgery, maternal diabetes, and preeclampsia are associated with SFN.^2,3 The disease is characterized by indurated, nonsuppurative, erythematous or violaceous mobile subcutaneous masses with taut overlying skin. The face, trunk, buttocks, and proximal extremities are the typical locations of lesions.⁴ Subcutaneous fat necrosis usually develops within the first several weeks of life, most frequently between the 5th and 10th days, and is usually self-limited. Hypercalcemia may be associated with SFN and represents the most serious complication; undetected hypercalcemia may have a fatal outcome. Other complications include nephrocalcinosis and nephrolithiasis.⁵ The pathogenesis of SFN is poorly understood, and in many affected infants no provocative factors have been identified. The disorder does not occur in all infants who are at risk.

The presence of growing masses in the soft tissues of the neonate should be carefully investigated. Differential diagnoses include rhabdomyosarcoma, aggressive fibromatosis, hemangioma, sclerema neonatorum, and fibrous lesions, including infantile myofibromatosis.^6,7

Magnetic resonance imaging characteristics of SFN are typical. Criteria include abnormal signal intensity of the subcutaneous fat, hypointensity on TI-weighted images, moderate hypointensity on T2-weighted images with poor TI-weighted postcontrast enhancement, and no mass effect.

Magnetic resonance imaging allows the diagnosis of SFN without performing more invasive procedures such as biopsy of the lesion or surgical repair. Parents may be reassured about the probability of complete spontaneous recovery from SFN.

Accepted for publication October 23, 2000.

Corresponding author and reprints: Carlo Bellini, MD, PhD, Servizio di Patologia Neonatale, Dipartimento di Pediatria, Universita di Genova, Istituto G. Gaslini, Largo G. Gaslini, 5, 16147 Genova, Italy (e-mail: carlobellini@ospedale.gaslini.ge.it).