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Idiopathic fat necrosis of scrotum: an important differential of childhood scrotal pain

We present the case of an 11-year-old boy who presented in winter with a one-day history of pain of the scrotum and bilateral testicular swelling. The onset of pain was in the context of prolonged exposure to cold water whilst swimming in a creek on his family property the day prior. His family home was located in the Central Highlands of Victoria, which is known to reach less than 10 air temperature on a typical winter’s day. He was systemically well and has no significant past medical history. On clinical examination, he was a mildly overweight boy with normally developed genitalia. He had significant bilateral scrotal swelling, with two palpable masses adjacent to the testis but separate to the scrotal skin. His testes and epididymides were unremarkable bilaterally. All his blood tests and urine dipstick were unremarkable. An ultrasound of the scrotum and testicles was performed (Fig. 1). Both testicles demonstrated normal size, echotexture and vascularity. There was hyperechoic soft tissue bilaterally within the scrotum, inferior and posterior to the testes, with mild blood flow, consistent with fat necrosis of the scrotum. He was managed conservatively with simple analgesia and he improved with no complications. Making a clear clinical diagnosis of acute scrotal pain in the prepubertal male is challenging. This is because paediatric presentations are varied and some clinical findings can be non-specific. Differentials for scrotal pain in children can include urological emergencies including testicular torsion, torsion of testicular appendage, epididymo-orchitis, inguino-scrotal hernia or testicular rupture. All children with acute scrotal pain should seek urgent review given the scope of the differentials. Historically diagnosis was only made on surgical exploration. Although first described in 1939, scrotal fat necrosis is still a rare diagnosis in boys, making up about 0.8% of all scrotal pain presentations. The aetiology of scrotal fat necrosis is unclear. Fat necrosis is common elsewhere in the body, for instance in the peritoneum or in the breast and the phenomena is often following trauma. Scrotal fat necrosis has been described as the consequence of cold exposure, as in our case. In patients with scrotal fat necrosis in the setting of cold exposure, there are two postulated causes for the injury. First, vasoconstriction leading to vascular occlusion and hypoxic cell injury, or direct cell necrosis due to the cold being a noxious stimuli. Previous studies have demonstrated the diagnosis histologically with evidence of fat necrosis and inflammatory infiltrates on histopathology. Most cases of idiopathic scrotal fat necrosis are reported in overweight, pre-pubertal boys. The pain has an acute onset of 48–72 h and is moderate in nature, sometimes causing wide based gait. There may be preceding mild, prolonged trauma from activities like riding a bike or exposure to the cold particularly after swimming in cold water. Boys with idiopathic scrotal fat necrosis are typically systemically well. There are classically discrete bilateral tender masses, located postero-inferiorly to and separate from the testicles, towards the median raphe of the scrotum. In rare cases the patient may present with unilateral mass. Examination of the testicles is usually unremarkable. Erythema on the scrotum, and the level of scrotal oedema is non-specific and varied. Like those in our case, blood investigations and urinalysis for this condition are always normal. Ultrasonography is a useful modality and should be a mainstay in investigating scrotal pain if testicular torsion has been ruled out. It is reported to be underused in some studies, with only 15% of scrotal pain presentations receiving pre-operative ultrasonography. Ultrasonography is particularly useful in diagnosing fat necrosis of the scrotum as there is a characteristic appearance. Fat necrosis of the scrotum appears on ultrasound as hyperechoic, posterior shadowing, located inferior to and separate to the testes. There can be increased Doppler vascularity in this area. There are also findings of normal testes and normal testicular blood flow. The natural history of idiopathic fat necrosis of the scrotum is self-resolution and does not require surgical exploration. Management should be conservative with analgesia and no antibiotics are