Leptomeningeal cyst

Last revised by Joshua Yap on 6 May 2024

Leptomeningeal cysts, also known as growing skull fractures, are an enlarging skull fracture that occurs near post-traumatic encephalomalacia. The term cyst is actually a misnomer, as it is not a cyst, but an extension of the encephalomalacia. Hence, it is usually seen a few months post-trauma.

The majority (approximately 90%) occur in children <3 years 8. They complicate ~1% of skull fractures 4,8

Children can present with 5:

The exact pathogenesis remains unclear 5 but it is thought they occur secondary to skull fractures causing dural tears allowing the leptomeninges and/or cerebral parenchyma to herniate into it 4. Pulsations from CSF erode the fracture margin, resulting in eventual expansion and non-union 6.

  • round or oval lucency with smooth margins 4

CT scan is the modality of choice for the evaluation of leptomeningeal cyst. It consists of a lytic calvarial lesion with scalloped edges, in which encephalomalacia invaginates. The following features may also be present 4,5

Treatment usually consists of craniotomy around the cranial defect, then suturing of the dura and apposition of the bone edges 7. The dural tear is expected to be larger than the bone fracture and may have advanced until it has reached a dural sinus. Hence, it is advised to prepare for bleeding from a sinus during surgery.

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