Acute Spontaneous Subaponeurotic Fluid Collection in a 3-month-old

A spontaneous subaponeurotic fluid collection (SSAFC) is a self-limiting fluid collection located beneath the scalp aponeurosis, typically appearing at around 8-16 weeks of age. Onset of SSAFC symptoms may cause concern for unique pathologies and require workup. A thorough history and exam is needed to help differentiate between a benign condition and a presentation which requires immediate neurosurgical intervention. Our case describes a 12-week-old female presenting with acute onset of a fluid collection on the scalp. Birth history was unremarkable, and there was no known history of acute trauma to explain the swelling. Workup included an ultrasound and a CT scan which revealed a left parietal subgaleal fluid collection and a partial fusion of the anterior most portion of the metopic suture. Physical exam, including neurological exam, was normal aside from the scalp findings. Neurosurgery was consulted but ultimately the fluid collection resolved on its own. She was diagnosed with SSAFC. Although SSAFCs are innocent and temporary, they may cause alarm to both parents and clinicians due to their size and sudden onset. It is important to quickly distinguish between SSAFCs and more concerning conditions when initially evaluating a fluid mass. Current literature has an underrepresentation of SSAFCs and their risk factors. This case report aims to draw attention to this rare condition.