Background
A subgaleal hematoma defines as an accumulation of blood in the subgaleal space, a potential space between the periosteum and the tough fibrous epicranial aponeurosis composed of loose connective tissue and an abundance of small emissary veins connecting the superficial scalp vein to the dural sinus; therefore, the haemorrhage is usually venous in nature (Figure 1d). The anatomic landmarks extend from the orbital ridge anteriorly to the nuchal ridge posteriorly to the temporal fascia laterally (Figures 1a, 1b, 1c). Because the subgaleal hematoma is superficial to the periosteum, it may cross cranial sutures.
Clinical and imaging perspective
Although it commonly occurs in the neonatal period following instrumental delivery [1], and trauma, physical abuse, or bleeding disorders are the other causes [2,3,4]. Apart from the above causes, the nonaccidental injury must also be ruled out in a very young child, as it can be a sign of child abuse. While massive subgaleal hematomas are often associated with significant head trauma in older children, they can also occur after minor trauma without underlying brain injury or bony fracture. This is due to the thin and pliable calvaria in a growing child, which can lead to shearing injury between the subgaleal layer and the aponeurosis of the occipitofrontalis muscle. This pliability makes the child more susceptible to subgaleal hematoma, even after minor trauma. The mechanism involves a radial or tangential force acting on the flexible or developing skull. This force is easily dissipated through the subgaleal potential space because of loose connective tissue, leading to rupturing of the emissary's veins and resulting in venous haemorrhage. The sutures do not confine this type of haemorrhage but, because of loose connective tissue, can spread rapidly till the anatomic limit of galea aponeurosis. Therefore, if massive, it can cause potentially life-threatening extracranial haemorrhage. The close differential diagnoses are cephalohematoma, delimited by sutures, and subcutaneous hematoma, which is superficial and localized because the skin tightly adheres to the galea. Imaging techniques play a vital role in diagnosis and delineation of extent. In most cases, the hematoma resolves spontaneously or with a compression bandage within a few weeks and does not require aspiration and drainage because the risk of infection outweighs the benefit [2].
Teaching points
- Children are not just mini-adults; the patterns of pediatric skull injury differ from adults because of their different physiology. An isolated massive subgaleal hematoma is rare after minor blunt trauma without underlying brain injury and bony fracture. However, the pliability of thin growing calvaria makes the child more susceptible to such massive subgaleal hematoma, even after a minor trauma.
- Imaging plays a crucial role in the diagnosis, delineation of extension, and treatment planning of subgaleal hematoma. A non-contract head CT is sufficient to diagnose the hematoma as a dense subgaleal collection that can cross the suture and extend rapidly to the anatomical limits of galea aponeurosis because of loose connective tissue.
- It is important to rule out nonaccidental injury in a very young child, as it can be a sign of child abuse.
- Reporting checklist must include the hematoma size, attenuation, extent, and the presence of an associated fracture or parenchymal brain injury.
