Pearls & Oy-sters: Dural defect repair as treatment for refractory headache from cerebrospinal fluid leak

Discussion

This was a suspected case of CSF leak secondary to a traumatic fall. CSF leak can lead to low CSF pressure and debilitating headaches.^1,2 MRI head with and without contrast may demonstrate features suggestive of low CSF pressure such as subdural hygromas, enhancement of the pachymeninges, engorgement of venous plexuses, pituitary hyperemia, and brain sagging. However, up to 20% of patients do not demonstrate the classic MRI abnormalities.¹

Numerous spinal manifestations of suspected low CSF pressure can be seen such as meningeal diverticula, extrathecal CSF collections, syringomyelia, and retrospinal C1-C2 fluid collections.¹ In our case, the radiographic features and location of the sacral canal fluid-intensity lesion could easily be mistaken as a Tarlov cyst, which was initially reported on the MRI. A Tarlov cyst is a CSF-filled nerve root cyst most commonly found at the sacral level and the exact cause of a Tarlov cyst is unknown. One theory is leakage of CSF into the nerve root sheath after a traumatic injury through an abnormal congenital connection between the subarachnoid space and the area surrounding the affected nerves (perineural region).³ A Tarlov cyst can become symptomatic and grow due to buildup of fluid from points of minoris resistentiae leading to compression to adjacent structures such as nerve roots. It can rarely be the cause of CSF leak if it ruptures into the extradural space.³ A spinal extradural arachnoid cyst can be caused by a rare small defect of the dura that leads to CSF accumulation and communication defects between the collection and the subarachnoid space.⁴ This is similar to meningeal diverticula in the thoracic spine as a result of protrusion of the arachnoid membrane through spontaneous dural tears and it can be associated with CSF leak.^1,4

It is difficult to distinguish between the 2 types of cysts or determine the location (intradural or extradural) through MRI alone. A CT or magnetic resonance (MR) myelogram could have provided more information. In our case, a dural defect was confirmed during surgery. It was causing leakage of CSF, which formed a collection in the sacral canal. The size of the collection was substantial and bone remodeling was demonstrated (figure, C and D), which may have accounted for our patient's back pain. This discovery has treatment implications as symptomatic sacral collections or cysts are sometimes managed through drainage. In our case, this could have resulted in worsening symptoms from lowering the CSF pressure further and recurrence of fluid collection in the context of an untreated dural defect.^3,5

This case illustrates the importance of making a diagnosis based on clinical–radiologic correlation. A CSF leak should be explored in patients with orthostatic headaches (worse upright) and lower back pain in the context of a sacral canal fluid-intensity lesion demonstrated on imaging. Advanced imaging modalities such as CT/MR myelogram or surgical exploration may be required to confirm a CSF leak. MRI head can be normal in cases of suspected low CSF pressure and MRI spine may not be effective in localizing a CSF leak. A misdiagnosis of a benign and simple sacral cyst could lead to suboptimal or inappropriate management. Identifying a dural defect and CSF leak can lead to appropriate intervention, such as targeting epidural patches at the site of leak, and prevent progression and morbidity.