Subcutaneous Fat Necrosis of the Newborn Workup

Updated: May 15, 2018
  • Author: Sungat K Grewal; Chief Editor: William D James, MD  more...
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Workup

Laboratory Studies

Screening for hypercalcemia is important since morbidity is far more likely to result from severe hypercalcemia than from the skin lesions of subcutaneous fat necrosis of the newborn (SFNN). A study by Shumer et al in 2014 found that 43% of infants with subcutaneous fat necrosis of the newborn and severe hypercalcemia (≥3 mmol/L before age 6 wk) were asymptomatic. [25] Calcium levels should be monitored at least biweekly [29] for several months. Shumer et al also reported that 6 of 7 infants with subcutaneous fat necrosis of the newborn and severe hypercalcemia had eosinophilia. [25]

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Imaging Studies

Imaging studies such as ultrasonography, computed tomography, and magnetic resonance imaging have been used to aid in the diagnosis but are not necessary to diagnose subcutaneous fat necrosis of the newborn (SFNN). [1, 30, 31, 32]

In the setting of hypercalcemia, imaging studies may be useful to document the extent of tissue calcification (eg, in nephrocalcinosis).

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Procedures

Skin biopsy that includes subcutaneous fat is the traditional way to make a diagnosis. Punch biopsy can be adequate as long as it harvests subcutaneous fat. It has also been suggested that fine-needle aspiration biopsy, which is minimally invasive and far quicker, can be just as accurate. [33]

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Histologic Findings

Key histological findings in subcutaneous fat necrosis of the newborn (SFNN) include fat lobule necrosis, crystallization of fat, and lipocytes present in a radial arrangement. [34]  Patchy areas of fat necrosis are surrounded by a granulomatous infiltrate of lymphocytes, macrophages, and giant cells. Many of the fat cells and giant cells contain needle-shaped clefts that often lie in a radial arrangement. Frozen sections reveal doubly refractive crystals that stain with oil red O. [1, 35] Small foci of calcium are scattered throughout the necrotic fat, and, sometimes, extensive areas of calcification may be present. Biopsy specimens of older lesions may demonstrate fibrosis. Reports have described multinucleated giant cells containing eosinophilic granules, perhaps released from surrounding degranulating eosinophils. [1, 36]

Fine-needle aspiration findings depend on the stage of evolution. Early stages show minimal inflammation and minimal necrosis. Fat cells have a crystalline shape. Later stages show more advanced necrosis, inflammation with phagocytosis of cellular debris, and crystallization. [33]

See the image below.

Histological slides of early and later stages of s Histological slides of early and later stages of subcutaneous fat necrosis of the newborn after fine-needle aspiration biopsy. Courtesy of Elsevier (Elston DM, Ferrringer T, Ko CJ, et al. Panniculitis. In: Dermatopathology. 2nd ed. Elsevier Limited; 2014:249-56).
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