Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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March 25, 2021
Growing Skull Fracture
- Background:
- Growing skull fracture, also known as posttraumatic bone absorption or leptomeningeal cyst, is a very rare complication of a traumatic brain injury.
- Ninety percent occur in children under 3 years of age.
- The proposed mechanism is that a tear of the dura mater coexists with the cranial fracture, allowing the meninges and/or the cerebral parenchyma to herniate through it. The CSF’s own pulsations appear to erode the margin of the fracture and expand it.
- Although it is often referred to as a “cyst,” it is not a true cyst, but focal herniation of an area of encephalomalacia.
- There are 3 types: leptomeningeal cyst, encephalocele, and porencephalic cyst.
- The growing fracture is usually seen a few months posttrauma.
- The most frequent location is the parietal bone.
- Clinical Presentation:
- Most common presentation is an enlarging scalp mass
- Other rarer presentations described in the literature include seizure and focal neurologic deficit such as hemiparesis.
- Key Diagnostic Features:
- Imaging is essential for the diagnosis. Ultrasound and skull radiography may show an enlarging fracture. CT confirms the diastatic fracture and brain herniation and demonstrates the extent of the intracranial pathology. MRI is more accurate in demonstrating the brain changes.
- Imaging findings in the leptomeningeal cyst include a lytic calvarial lesion with scalloped edges and herniating encephalomalacia, which follows CSF signal on all MRI sequences.
- When the herniated brain tissue does not show malacia, the term "encephalocele" can be used, which may be seen as damaged or gliotic brain.
- In some cases, a porencephalic cyst may develop, described as a well-defined intracranial cystic lesion that follows CSF signal on MRI sequences, communicates with the ventricular system, and in the context of a skull defect, may extend into the subgaleal space.
- Differential Diagnoses:
- Posttraumatic intradiploic leptomeningeal cyst (PTIDLC): It only shows a fracture of the inner table and laceration/tear of the dura mater with accumulation of CSF in a sac situated within the diploic space. It is most frequently in the occipital region.
- Intradiploic arachnoid cyst: Imaging features are the same as PTIDLC, but it usually presents late in life and is formed due to obstruction to the flow of CSF from the arachnoid granulations into the venous system, without a history of trauma.
-
Osteolytic lesions (metastasis, epidermoid cyst, eosinophilic granuloma, myeloma): Lytic lesions on skull radiography can resemble the lytic image that a leptomeningeal cyst may show. However, CT and MRI would rule out these lesions that behave like diploic lesions and would demonstrate the absence of a skull fracture. There will also be no history of trauma.
- Treatment:
- Treatment usually includes the excision of the cyst, dural closure, and repair of the bone defect.
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