1. RADIOLOGICAL FINDINGS
DIAGNOSTIC KEY.
CLASSIC TRIAD: - Diffuse Dural Enhancement/thickness.
- Subdural effusion/hematoma/hygroma.
- Downward displacement of the brain.
***The absence of one of the previously mentioned signs (classic) does not exclude this entity. 1

2. CLASSIC FINDINGS
CT FINDINGS.

3. CT FINDINGS.
In general we should not make a CT in a patient with suspicion of a SIH. Nevertheless, in some circumstances CT is made urgently if the patient is getting worse for example, to try to rule out complications. Classically there are some described signs on CT that are explained as follows:
SUPRASELLAR CISTERN OBLITERATION.
CT CAN BE NORMAL.
+/- DURAL THICKNESS.
+/- BILATERAL SUBDURAL LIQUID COLLECTIONS (effusion, hematoma).
CT on a puerpera with SIH a few days after epidural anesthesia.
Subdural effusions.
Puerpera with SHI. Suprasellar cistern obliteration.
MIDLINE ATRIUM DEVIATION.
DIFFUSE PACHYMENINGEAL ENHANCEMENT with iv contrast. 3

4. CLASSICS FINDINGS
BRAIN MR FINDINGS.

5. BRAIN MR FINDINGS
PITUITARY GLAND ENLARGEMENT (+1.5 of normal size). This sign is not very sensitive in pregnant or puerperal women.
SAGITTAL T1
Three patients with SIH and significant enlargement on hypophysis size (more than 1.5 of her normal size).
BRAIN DESCENT(40-50%).
Downward displacement of cerebellar tonsils (25%- 75%). “Sagging midbrain” (descent midbrain). Basal cisterns obliteration.
An example of downward displacement of cerebellar tonsils and sagging midbrain.

6. BRAIN MR FINDINGS SAGITTAL T1
“FAT-MIDBRAIN”. “SUNKED OR DRAINED MIDBRAIN”. Midbrain and pons morphology distortion. They can appear enlarged or with an abnormal morphology. Sometimes a distortion of the anterior pons edge can be seen. The midbrain can even imprint on the dorsum sellae and the pons against the clivus. A B
Three patients with SIH. A. There is a bulge of pons (fat midbrain). B. Anomalous morphology of midbrain and pons.
NORMAL 6

7. BRAIN MR FINDINGS T2 and FLAIR
SUBDURAL FLUID COLLECTIONS. Effusions can occur and less frequently also subdural hematoma. Collections are usually bilateral and normally thin, with a maximum thickness between 2-7 mm. It is more probable to detect little quantities of fluid with Flair sequences than T2WI, because Flair sequences provide more contrast.
Puerpera with SHI after epidural anesthesia. In this case the collection was subtle and it could be detected with Flair sequence.
Coronal T2 sequence in a patient with hydrocephalus who later presented with SIH. Obvious subdural collections.
Axial T2 sequence in a patient with SIH. Subdural effusions. 7

8. BRAIN MR FINDINGS T2 and FLAIR
SUPRASELLAR CISTERN OBLITERATION. This finding is very rare, it usually occurs when the clinic has evolved in time.
DECREASE ON LATERAL VENTRICLE SIZE. This is not an early finding either, although it is possible to see it in some cases. Midline atrium deviation is common too.
Axial Flair and T2 sequences in a patient with a traumatic injury after epidural anesthesia and two hematic patchs without success. Decrease on lateral ventricule size, frontal horns overall. 8

9. BRAIN MR FINDINGS
T1 iv contrast.
DIFFUSE AND INTENSE DURAL ENHANCEMENT (85%). This the most common sign in these patients and it is included in the diagnosis criteria of “The International Clasification of Headache Disorders”.
3D T1 with gadolinium sequence. It shows a diffuse and intense enhancement of the dura. With this sequence it is possible to assess the different planes of space too. 9

10. NEW RADIOLOGIC SIGNS
BRAIN MR FINDINGS.

11. BRAIN MR FINDINGS SAGITTAL T1
“VENOUS DISTENSION SIGN” (VDS). It is one of the earliest signs that we can find in these patients. This sign consists in a characteristic change in the contour of the dural sinuses secondary to the dural sinuses compensatory enlargement. A convex bulging of the inferior border of the middle third in the dominant transverse sinus is observed.
Normal contour of the dominant transverse sinus. Magnified images of boxed area (middle third). The last image is a schematic representation of the inferior border of the transverse sinus where the dotted line depicts the distended, convex, lower border of the middle third of the dominant transverse sinus as seen in intracranial hypotension.
MR.I. Farb, R. Forghani. Diagnosis and Temporal Evolution of Signs of Intracranial Hypotension on MRI of the brain. Neuroradiology :
MR.I. Farb, R. Forghani, S.K. Lee, D.J. Mikulis, and R. Agid. The Venous Distension Sign: A Diagnostic Sign of Intracranial Hypotension at MR Imaging of the Brain. AJNR Am. J. Neuroradiol., Sep 2007; 28: 11

12. BRAIN MR FINDINGS SAGITTAL T1
**It is the first sign that normalizes after appropriate treatment. This sign could be used as a predictor of treatment success, which would be very useful especially in patients whose clinical improvement is doubtful once the treatment is established.
The non-detection of this sign after treatment does not imply any response. It must have a pretreatment MRI to compare the evolution.
Examples of “VDS” in two patients, before and after treatment.
Another two examples of “VDS” in two patients before treatment.
MR.I. Farb, R. Forghani. Diagnosis and Temporal Evolution of Signs of Intracranial Hypotension on MRI of the brain. Neuroradiology :
MR.I. Farb, R. Forghani, S.K. Lee, D.J. Mikulis, and R. Agid. The Venous Distension Sign: A Diagnostic Sign of Intracranial Hypotension at MR Imaging of the Brain. AJNR Am. J. Neuroradiol., Sep 2007; 28: 12

13. BRAIN MR FINDINGS T2 and FLAIR
DIFFUSE PACHYMENINGEAL HYPERINTENSITY BY FLAIR. It is less sensitive than gadolinium enhancement and disappears early in the clinical course (before the pachymeningeal enhancement). However, it can be very useful because Flair is a fast and accessible sequence, included in most MRI protocols regardless of clinical suspicion. In this sequence it is not necessary to use contrast, so it will have a particular value in situations where it is not possible to use it (allergies, non-availability, ...).
Patient with no clinical suspicion of SHI, an MR without contrast was performed. Axial Flair sequence and magnified image depict diffuse pachymeningeal hyperintensity.
M. Tosaka, N. Sato, H. Fujimaki, Y. Tanaka, K. Kagoshima, A. Takahashi, N. Saito, and Y. Yoshimoto. Diffuse Pachymeningeal Hyperintensity and Subdural Effusion/Hematoma Detected by Fluid-Attenuated Inversion Recovery MR Imaging in Patients with Spontaneous Intracranial Hypotension. AJNR Am. J. Neuroradiol., Jun 2008; 29: 13

14. BRAIN MR FINDINGS T2 and FLAIR
In Flair sequences the signal intensity of cerebrospinal fluid (CSF) is void, resulting in an excellent definition of both brain and sulcus and a great contrast to the lesions located in areas close to CSF. This method is the same we often use to detect meningeal lesions such as subarachnoid hemorrhage and meningitis.
Therefore, the sequence Flair may be optimal to evaluate meningeal thickening associated with the SHI, as well as to detect small effusions located very close to the subarachnoid space as mentioned above.
-M. Tosaka, N. Sato, H. Fujimaki, Y. Tanaka, K. Kagoshima, A. Takahashi, N. Saito, and Y. Yoshimoto. Diffuse Pachymeningeal Hyperintensity and Subdural Effusion/Hematoma Detected by Fluid-Attenuated Inversion Recovery MR Imaging in Patients with Spontaneous Intracranial Hypotension. AJNR Am. J. Neuroradiol., Jun 2008; 29: 14

15. BRAIN MR FINDINGS T2 and FLAIR
RELATIVE DECREASE IN SIGNAL INTENSITY OF SUBCORTICAL WHITE MATTER ON FLAIR IMAGES (and T2) PREVIOUS TREATMENT. Subsequently, when the symptoms improve, this sign disappears on MR.
Patient with suspicion of SIH.
The relative decrease in signal intensity of white matter is not always observable in the visual assessment, although in this case it is quite obvious because it has forced the window. That is why the relative decrease in signal has been described in terms of a ratio that is calculated in relation to the adjacent cortex.
This decrease is due to increased deoxyhemoglobin caused by venous stasis that also affects spinal veins, especially in the white matter.
It is not always observable in the visual analysis. Therefore it has been described in terms of a ratio that is estimated depending on white matter and adjacent cortex.
-M. Adachi, S. Mugikura, A. Shibata, E. Kawaguchi, T. Sato, and S. Takahashi
Relative Decrease in Signal Intensity of Subcortical White Matter in Spontaneous Intracranial Hypotension on Fluid-Attenuated Inversion Recovery Images
AJNR Am. J. Neuroradiol., first published on Mar 6, 2009 as doi: doi: /ajnr.A1498 15

16. BRAIN MR FINDINGS T2 and FLAIR
The relative decrease in signal was described by calculating a ratio which is the quotient between a ROI placed in the white matter affected and the other ROI in the gray matter of the adjacent cortex.
Axial Flair sequence in a patient with SIH. Example of calculation of the ratio to assess the relative decrease of signal in white matter respecting adjacent cortex. The value obtained is approximately 0.7, consistent with the values described in SIH.
-M. Adachi, S. Mugikura, A. Shibata, E. Kawaguchi, T. Sato, and S. Takahashi
Relative Decrease in Signal Intensity of Subcortical White Matter in Spontaneous Intracranial Hypotension on Fluid-Attenuated Inversion Recovery Images
AJNR Am. J. Neuroradiol., first published on Mar 6, 2009 as doi: doi: /ajnr.A1498 16

17. SPINAL MR FINDINGS.

18. SPINAL MR FINDINGS
***SIH is usually caused by a leak of CSF through the spinal dural sac, so the spinal MR must show abnormal findings with high frequency. However, the “International Classification of Headache Disorders” does not include the spinal MR findings. Nevertheless, there are specific signs on spinal MR that suggest spinal SIH, so it has great value in doubtful cases or when there are few signs on brain MR.
Fat saturation T2 (FatSat T2) sequences must be performed in both axial and sagittal planes, in cervical, thoracic or lumbar level.

19. SPINAL MR FINDINGS FATSAT-T2
DISTENTION OF THE ANTERIOR SPINAL EPIDURAL VEINS AT THE UPPER CERVICAL REGION.
The distention of the spinal epidural veins is detected as two prominent signal-intensity flow voids in the antero-lateral epidural space.
The size of the anterior epidural venous plexus gradually increased (maximum at L4-L5), so an extensive plexus in the cervical region should be considered abnormal.
A. Watanabe, T. Horikoshi, M. Uchida, H. Koizumi, T. Yagishita, H. Kinouchi. Diagnostic Value of Spinal MR Imaging in Spontaneous Intracranial Hypotension Syndrome. AJNR Am J Neuroradiol 30:147-51/ Jan 2009 19

20. The dural sac collapses, its outline taking a hexagonal morphology.
SPINAL MR FINDINGS
FATSAT-T2
COLLAPSED DURAL SAC. (Hexagon-like contour appearance, “festooned appearance”).
The dural sac collapses, its outline taking a hexagonal morphology.
A. Watanabe, T. Horikoshi, M. Uchida, H. Koizumi, T. Yagishita, H. Kinouchi. Diagnostic Value of Spinal MR Imaging in Spontaneous Intracranial Hypotension Syndrome. AJNR Am J Neuroradiol 30:147-51/ Jan 2009 20

21. SPINAL MR FINDINGS FATSAT-T2
EPIDURAL COLLECTIONS. It is in the thoracic region that these collections are bigger and better visualized. The thoracic region is the most frequent site for leak location.
Depending on the region, collections stand with higher predisposition in a specific location.
- Cervical: anterior location.
- Thoracic: posterior location.
- Lumbar: peripheral. A B A
Two patients with SIH.A and B. Both presenting with typical epidural posterior collections in dorsal spine. 21

22. SPINAL MR FINDINGS FATSAT-T2
DISTENTION OF THE ANTERIOR SPINAL EPIDURAL VEINS IN SAGITTAL SEQUENCES. Winding signal-intensity flow voids of the dilated epidural veins behind the vertebral bodies on the parasagittal plane.
DISTENTION OF THE THORACO-LUMBAR ANTERIOR SPINAL EPIDURAL VEINS. Prominent signal-intensity flow voids in the anterior epidural space.
COLLECTIONS AROUND THE NERVE ROOTS AND PARAVERTEBRAL SOFT TISSUES. Hyperintensity observed in the output of the nerve roots due to the accumulation of CSF, and only seen in sequences with fat suppression.
Patient with SIH. Slight hyperintensity in the output of the nerve roots.
A. Watanabe, T. Horikoshi, M. Uchida, H. Koizumi, T. Yagishita, H. Kinouchi. Diagnostic Value of Spinal MR Imaging in Spontaneous Intracranial Hypotension Syndrome. AJNR Am J Neuroradiol 30:147-51/ Jan 2009 22