Subcutaneous fat necrosis of the newborn

Clinical History

A female neonate delivered via emergency caesarean section at 36 weeks of a twin gestation, due to fetal distress, requiring peripartum assisted ventilation, developed on the 13th day of life two well-defined hard nodules in the medial surfaces of the right arm and the right leg.

Imaging Findings

An initial ultrasound (Fig. 1) of the right upper and lower extremities showed a focal ill-defined thickening and heterogeneity of the subcutaneous tissue, mainly hyperechoic with central areas of decreased echogenicity and deep attenuation. The adjacent muscles had a normal appearance and there were no oedemas or fluid collections.
Limbs radiographies (Fig. 2) were then performed and revealed soft tissue thickening and amorphous calcification. The underlying bone was unremarkable.
During the first week, on the follow-up ultrasound, the calcifications started to become denser and more defined and progressively decreased in size during the first three months, until complete resolution (Fig. 3).

Discussion

Subcutaneous fat necrosis of the newborn (SCFN) is an uncommon, transient inflammatory disorder of adipose tissue (panniculitis), found in full or post-term neonates.
The aetiology of SCFN is unclear but several associated factors have been reported: perinatal stress (asphyxia, peripheral hypoxemia, hypothermia, meconium aspiration or trauma) [1, 2] and maternal factors (pre-eclampsia, gestational diabetes or maternal exposure to cocaine or calcium antagonists) [2, 3]. It is presumed that these lesions result from tissue hypoxia as it augments the deposits of saturated fatty acids, which have a higher melting point, leading to crystallization and fat necrosis. Pressure injury and cooling are also factors that have been associated with increased risk of necrosis. [4, 5]
Skin lesions are characterized by hard, mobile, erythematous or violaceous subcutaneous nodules or plaques. Typically, lesions develop on the face, trunk and buttocks, as well as legs and arms near the trunk. These nodules present in the newborn several weeks after birth and resolve spontaneously over a period of weeks to months [2, 3].
Although SCFN is often benign and self-limited, it can cause significant complications. Rare local complications include epidermal atrophy, ulceration, scarring, or infection. Several haematological and metabolic alterations have been described in association with SCFN including thrombocytopenia, hypoglycaemia, hypertriglyceridaemia, anaemia, and most importantly, hypercalcaemia [2, 3]. Hypercalcaemia can have a fatal outcome and may occur from 1 month to 6 months after the skin lesions develop, so any neonate with SCFN should have serum calcium levels monitored for 6 months.
SCFN has been increasingly described as having distinctive radiological findings. SCFN can cause soft-tissue calcification. The use of imaging, namely radiography, to identify calcium in the lesion can help narrow the differential diagnosis. At US this entity shows areas of increased echogenicity [1, 5]. CT shows hypervascular masses immediately deep to the skin ranging from diffuse subcutaneous thickening to discrete nodules [5, 7]. On MR, the lesions are iso to hypointense on T1 and hyperintense on T2 and fat-suppressed T2 -weighted images [1, 5]. Knowledge of imaging features of SCFN can help distinguish this unusual entity from other benign and malignant lesions, and preclude an unnecessary biopsy or surgery.
The hypothesis of SCFN was considered after the first ultrasound; the initial diagnostic workup showed hypercalcaemia (14, 9 mg/L) that resolved spontaneously. Given the favourable clinical and ultrasonographic evolution the diagnosis of SCFN was inferred, a biopsy was not performed and the workup was ended.

Differential Diagnosis List

Final Diagnosis

Subcutaneous fat necrosis of the newborn

URL:	https://www.eurorad.org/case/11290
DOI:	10.1594/EURORAD/CASE.11290
ISSN:	1563-4086