Spontaneous subaponeurotic fluid collection in an infant: illustrative case.

backgroundSpontaneous subaponeurotic fluid collections (SSFCs) are benign, typically self-limiting fluid collections beneath the scalp's aponeurosis. Their abrupt onset and unusual appearance can cause significant alarm and suspicion of considerable pathology or child abuse. With an unclear etiology and concerning clinical presentation, it is important to recognize SSFCs as a unique condition, distinct from those that require immediate neurosurgical intervention. OBSERVATIONS: A 10-week-old male presented with soft, nontender, fluctuant scalp swelling with a fluid thrill in the left lateral occipitoparietal region, not confined by suture lines and without bruising or erythema. He had been delivered vaginally after 6 hours of labor and had been monitored with a fetal scalp electrode. No scalp swelling or fluid collections, injury, trauma, or hair manipulation had been noted from the immediate neonatal period until the current presentation. This fluid collection was subsequently identified as an SSFC, which resolved within 24 hours precluding the scheduled ultrasound. LESSONS: Despite their benign and transient nature, SSFCs might raise suspicions of child abuse or more severe conditions requiring immediate neurosurgical intervention. Although their exact pathophysiology and etiology remain unclear, SSFCs typically resolve spontaneously, with no additional diagnostic workup or management necessary following adequate differentiation from other conditions. https://thejns.org/doi/10.3171/CASE24589.