Cellulitis, a diffuse inflammation of connective tissue with severe inflammation of dermal and subcutaneous layers of the skin, is a common lesion in children, usually responsive to systemic antibiotic therapy. However, an unusual course of healing or some nontypical features should call the treating physician to consider and investigate for other diagnoses that might prevent unnecessary treatment and alleviate parental stress. We present a case of posttraumatic fat necrosis, demonstrating some pitfalls in the process of diagnosis.
Posttraumatic fat necrosis of the subcutaneous fat tissue can occur following a fall, blunt injury, surgery, and minor procedures such as injections [
A 9-year-old girl was admitted to the Emergency Department 4 days after a blunt trauma in her left leg. On admission the patient had no fever. On physical examination, there was an area of edema, warmth, erythema, and tenderness with indistinctive margins on the anteromedial aspect of the left leg.
The rest of the physical examination was normal except for obesity and her history was unremarkable. X-ray of the leg was normal. She was clinically diagnosed as having cellulitis and was discharged with oral amoxicillin/clavulonic acid. However, edema, warmth, erythema, and tenderness of the leg persisted for 2 more days, denoting no improvement and the patient was readmitted 2 days later to the Pediatrics Department. Oral antibiotic was replaced with intravenous therapy (amoxicillin/clavulanic acid 75 mg/kg/day).
Laboratory findings were white blood cell count 13.6 × 103/
The antibiotic therapy was changed 4 days later to cloxacillin (100 mg/kg/day) and ampicillin (100 mg/kg/day) because of unsatisfying improvement.
Gradual improvement occurred over the next two days; edema, warmth and erythema became mild and the tenderness disappeared. The patient was discharged 6 days after her admission with oral cephalexin (35 mg/kg/day).
Physical examination on a scheduled outpatient visit three days after discharge revealed erythema and induration of the skin of the left leg without tenderness or edema laboratory findings were within normal range. Ultrasound of the left shin demonstrated swelling of the soft tissue in the anteromedial aspect with a number of hypoechoic collections, the biggest one was 0.9 × 2.13 × 2 cm, margins were indistinctive with unclear fluid, blood supply was not increased, and the bones were intact, thus excluding the possibility of osteomyelitis (Figure
Ultrasound doppler 14 days after trauma. The investigation was targeted to the distal part of the shin. A complex process is seen in the subcutaneous fat with hyper- and hypoechoic regions and unclear boundaries without increased blood flow and without periosteal reaction.
Two months after admission, MRI demonstrated edema of the subcutaneous fat medially to the tibial bone with thickening of the subcutaneous septations and unclear boundaries. There was no involvement of bone cortex or marrow and no enhancement was evident (Figure
(a) MRI-T1 tirm and (b) MRI-T1. Coronal slices of the distal part of shin with cutaneous tag. MRI findings were edema in subcutaneous fat medial to tibial bone with thickening of subcutaneous septations and unclear boundaries, without involvement of bone cortex or marrow. T2-weighed images did not add information and are not shown.
Follow-up ultrasound 3 month after trauma showed resolution of soft tissue edema with organization of echogenic (fatty) lesion surround by hypoechoic lesion (Figure
Ultrasound doppler 3 months after trauma. Resolution of the soft tissue edema: hyperechoic (fatty) lesion with hypoechoic halo with relatively clear boundaries. No periosteal reaction was noted.
Posttraumatic fat necrosis is quite prevalent, especially in the pediatric age group where minor trauma is a normal and common event, making this population more prone to this condition [
Most cases of posttraumatic fat necrosis appear as a palpable lump or as a local depression [
The index case appeared with edema, warmth, erythema and tenderness—a clinical picture similar to cellulitis. Our patient had a prolonged duration of symptoms uncharacteristic of cellulitis. In a patient with cellulitis, a symptomatic improvement is expected within 24–48 hours of the beginning of therapy and a visible improvement within 72 hours. Persistence of symptoms or signs after the expected time prompts further evaluation and imaging of the affected area to rule out other possible diagnoses such as subcutaneous fat necrosis, tumors such as lymphoma, sarcoma, chloroma and early stages of necrotizing fasciitis and other rare infections.
The appearance of our patient resembles that of earlier descriptions with gender distribution, typical location of lesion and recent history of trauma, and is different in that there is lack of a lump or depression at the site of the lesion. An alternative diagnosis that could explain these differences could be cellulitis with an extension to deeper layers, also known as infectious panniculitis. Primary infection can result from a pathogen introduced directly into the subcutaneous tissue through a penetration of the skin [