Overview of Spontaneous Intracranial Hypotension and Differential Diagnosis with Chiari I Malformation

Abstract

Spontaneous intracranial hypotension (SIH) occurs due to a leakage of the cerebrospinal fluid (CSF) lowering the pressure of subarachnoid space, mostly caused by a dural breach or discogenic microspur. As a result of less support provided by CSF pressure, intracranial structures are stretched downward, leading to a constellation of more or less typical MRI findings, including venous congestion, subdural effusions, brainstem sagging and low-lying cerebellar tonsils. Clinic examination and an MRI are usually enough to allow for the diagnosis; however, finding the location of the dural tear is challenging. SIH shares some MRI features with Chiari malformation type I (CM1), especially low-lying cerebellar tonsils. Since SIH is likely underdiagnosed, these findings could be interpreted as signs of CM1, leading to a misdiagnosis and an incorrect treatment pathway. Medical treatment, including steroids, bed rest, hydration caffeine, and a blind epidural blood patch, have been used in this condition with variable success rates. For some years, CSF venous fistulas have been described as the cause of SIH, and a specific diagnostic and therapeutic pathway have been proposed. The current literature on SIH with a focus on diagnosis, treatment, and differential diagnosis with CM1, is reviewed and discussed.

Keywords: Chiari malformation type I (CM1); myelographic imaging techniques; spontaneous intracranial hypotension (SIH).

Figure 1

Prone myelography (A) showing a regular ventral profile of the dural sac (arrows) with anterior extravasation at C5–C6 into the epidural space (arrows with dot). Myelo-CT ((B,C): sagittal and axial planes) shows the presence of a C5–C6 disc herniation, with an osteophyte (bone spur) of the upper somatic margin of C6 (arrows), in the right paramedian site, probable cause of the dural tear (the red line indicates in image (B) the axial plane of image (C) while in image (C) the sagittal plane of image (B)). Myelo-CT (D) also shows the presence of contrast in the epidural space (arrow with dot), anterior to the dural sac (arrow).

Figure 2

FLAIR sequence MRI showing low-lying cerebellar tonsils, which can lead to a misdiagnosis between SIH and Chiari malformation type I (A). Other MRI findings from the same patient are visible in Figure 3: clinical–radiological diagnosis of SIH is made and the patient is treated with an EBP. Resolution of the low-lying cerebellar tonsils was observed at the 12-month MRI follow-up (B).

Figure 3

Smooth and diffuse pachymeningeal enhancement (arrows) in a post-gadolinium MRI ((A,B): sagittal and coronal planes): the most sensitive intracranial sign pointing toward SIH. Cervicodorsal spine MRI (C) showing the presence of a spinal longitudinal extradural collection (SLEC) (arrows), which is a specific sign of SIH with dural mechanical tears along the thecal sac.