Reversible Syringomyelia in Spontaneous Intracranial Hypotension

Dear Editor,

Spontaneous intracranial hypotension (SIH) is characterized by orthostatic headache caused by cerebrospinal fluid (CSF) leakage or low CSF pressure, and brain magnetic resonance imaging (MRI) abnormalities such as diffuse pachymeningeal enhancement, venous engorgement, enlarged pituitary gland, and brain sagging.1 However, syringomyelia development has been rarely described in patients with SIH.2, 3, 4, 5, 6, 7 We present a case of SIH with reversible syringomyelia that did not require an epidural blood patch.

A 32-year-old female visited our clinic with a 2-month history of headache, ear fullness, and tinnitus. The headache onset was sudden, with no history of trauma or spinal intervention. The headache was positional, exacerbated to a Numeric Pain Rating Scale score of 8–9 by sitting or standing, and relieved to a score of 2–3 within minutes by lying down. Her body mass index was 23 kg/m². The findings of a neurological examination were unremarkable, including intact mental status, as were those of cranial nerve, sensory, and motor examinations, with a normoactive deep tendon reflex. Laboratory tests were also unremarkable, including normal erythrocyte sedimentation rate (3 mm/hour) and C-reactive protein (0.1 mg/dL). Serum anti-aquaporin-4 antibody, anti-myelin oligodendrocyte glycoprotein antibody, antinuclear antibody, and antineutrophil cytoplasmic antibody were also negative. The CSF profile was normal (nucleated cells, 2 cells/µL; protein, 30.8 mg/dL; oligoclonal bands, negative), and the CSF opening pressure was 10 cmH₂O. Brain MRI revealed pituitary gland enlargement, dural sinus engorgement, and tonsillar herniation compatible with SIH (Fig. 1A). MR myelography revealed CSF leakage at the C1–C2 and multiple lumbar levels (Fig. 1B and C), T2 hyperintensities at the C5–T2 levels indicating interstitial spinal cord edema associated with hydrosyrinx, and obex stenosis (Fig. 1D and E). The findings of a nerve conduction study, electromyography, and motor- and sensory-evoked potential tests were also normal. The headache severity gradually decreased throughout the course of her illness, so she chose conservative management over an epidural blood patch. Her headache had improved at the 4-month follow-up, and MR myelography revealed that the CSF leak, obex stenosis, and syringomyelia had disappeared (Fig. 1F-I).

Fig. 1
Baseline and follow-up magnetic resonance imaging findings. A: Sagittal T1-weighted, contrast-enhanced image showing pituitary enlargement, dural sinus engorgement, and tonsillar herniation below the foramen magnum (dashed line). B and C: Myelogram showing CSF leakage (arrows) at the cervical and lumbar levels. D: Sagittal T2-weighted image showing syrinx with spinal cord edema (arrow). E: Axial T2-weighted image showing obex stenosis (arrow). F-I: Improved obex stenosis, CSF leakage, and cord signal changes. CSF, cerebrospinal fluid.

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In addition to the current case, only a few cases of syringomyelia have been described in patients with SIH.2, 3, 4, 5, 6, 7 A recent study that compared groups of patients with SIH indicated that the main distinction between those with and without syrinx development was obex displacement below the foramen magnum.8 The authors hypothesized that Chiari-like cerebellar tonsillar herniation and foramen magnum crowding affect syrinx development in patients with SIH. Partial obstruction of the CSF pathways at the foramen magnum with obex stenosis may impair CSF hemodynamics, causing fluid to accumulate within the central canal and subsequently forming a syrinx with congenital Chiari type 1 malformation and acquired Chiari malformation due to SIH.8

Our case exhibited characteristics that were notable relative to previously reported ones.2, 3, 4, 5, 6, 7 In contrast to previous reports in which the syrinx improved after treatment, the syringomyelia in our case resolved through only conservative management. Syringomyelia was also confirmed in MRI performed 2 months after sudden headache onset, in contrast to the much later manifestation in previous cases (4 months to 10 years). Given that 30% of patients with SIH recover with conservative treatment,1 we speculate that the CSF leakage in our case was sufficient to impair CSF hemodynamics through tonsillar herniation and obex stenosis, which led to spinal cord edema that was visible in the presyrinx state,9 which then spontaneously healed. CSF leak, tonsillar descent, and obex stenosis were recovered with the resolution of syringomyelia in the follow-up MRI, which supported our speculation. These findings were consistent with those of previous reports.2, 3, 4, 5, 6, 7, 8

The near-normal CSF pressure in our case was not unexpected, since several studies have found that approximately 30% of patients with SIH have normal lumbar-puncture opening pressures.1 The craniospinal pressure gradient appears to be more critical in the pathogenesis of syrinx in the context of SIH than the absolute decrease in spinal CSF pressure. This speculation was further supported by the notion that syrinx development in the presence of a Chiari malformation is caused by an enhanced pressure wave delivered through the central canal of the spinal cord during systole.10

Our case demonstrated the rarely observed spinal MRI finding of syringomyelia in SIH, which might have been caused by the CSF pathways being obstructed at the foramen magnum due to SIH-induced brain sagging. Given that misdiagnosis can lead to unnecessary treatment, it is important to note that SIH can resemble the imaging features of Chiari type 1 malformation, and share pathophysiology similar to impaired CSF hemodynamics at the foramen magnum.