Postural headache
BMJ 2009; 338 doi: https://doi.org/10.1136/bmj.b911 (Published 19 March 2009) Cite this as: BMJ 2009;338:b911
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Sir
With reference to the endgame titled ‘Postural Headache’ (BMJ
2009;338:b911) we would like to point out several inaccuracies in the case
presentation and discussion that can be potentially misleading.
There are a few minor inaccuracies in the captions of the figures;
figure 1 is a fluid attenuation inversion recovery (FLAIR) sequence rather
than T2 weighted sequence (i.e designed to suppress the normal CSF) and
figure 2 is a T1 weighted sequence rather than T2 weighted (in a normal T2
weighted sequence the CSF is bright).
Although spontaneous intracranial hypotension is characteristically
associated with subdural collections, most patients have subdural hygromas
rather than haemorrhages.(1-3). The subdural collections present in this
case (figure 1) would be better characterised as subdural effusions with
the bright signal on FLAIR due to the characteristic proteinacious
content.
Pachymeningeal enhancement appears to be the most common feature on
MRI (4). The venous engorgement is difficult to evaluate on the images
supplied and without contrast. Certainly most radiologists wouldn’t have
characterised the superior sagittal sinus in figure 1 as engorged. The
venous engorgement is often easier to appreciate in the spinal epidural
venous plexus (5).
Downwards displacement of the brain is radiologically identified when
the position of the iter (opening of the aqueduct) lies below the
incisural line (connecting the anterior clinoid process and the venous
confluence) or when the tonsillar position lies more than 5mm below the
foramen magnum. Although there is sagging of the midbrain and there may be
some pontine flattening, the cerebellar tonsils are not protruded through
the foramen magnum on the image given (figure 2).
Finally, regarding the investigation of suspected cases, MRI would be
the examination of choice in most centres (as supplied by the authors of
the article – figure 3). CT myelography is invasive and not commonly
performed as the investigation of choice in order to find the CSF leak in
the UK. An MRI with or without intrathecal contrast or a radionuclide
cisternography may also be used as second line investigation (6).
It would be most valuable to entrust image interpretation to experts
when submitting teaching material with a major radiological content. We
would advocate consulting a radiologist to proof read submissions
involving radiological images and to consider having a radiologist as an
author if the article is centered around radiological images.
1. Schievink WI. Spontaneous spinal cerebrospinal fluid leaks and
intracranial hypotension. JAMA 2006;295:2284-96
2. Schievink WI, Maya MM, Moser FG, Tourje J Spectrum of subdural
fluid collections in spontaneous intracranial hypotension. J Neurosurg.
2005 Oct;103(4):608-13.
3. Lai TH, Fuh JL, Lirng JF, Tsai PH, Wang SJ. Subdural haematoma in
patients with spontaneous intracranial hypotension. Cephalalgia. 2007
Feb;27(2):133-8.
4. Su CS, Lan MY, Chang YY, Lin WC, Liu KT Clinical features,
neuroimaging and treatment of spontaneous intracranial hypotension and
magnetic resonance imaging evidence of blind epidural blood patch. Eur
Neurol. 2009;61(5):301-7
5. Wolfe SQ, Bhatia S, Green B, Ragheb J Engorged epidural venous
plexus and cervical myelopathy due to cerebrospinal fluid overdrainage: a
rare complication of ventricular shunts. Case report. J Neurosurg. 2007
Mar;106(3 Suppl):227-31
6. Liong WC, Constantinescu CS, Jaspan T Intrathecal gadolinium-
enhanced magnetic resonance myelography in the detection of CSF leak.
Neurology. 2006 Oct 24;67(8):1522
Competing interests:
None declared
Competing interests: No competing interests
Entrusting Image Interpretation to Radiologists?
Dear respondents,
Thank you for your recent letter in response to our article. Herein
we hope to clarify some valid points you raised.
It is important to note that FLAIR sequence and T2 –weighted are not
mutually exclusive terms. The images are T2 weighted. As you are aware T2
weighting are generated when there is as long (> 2000ms) interval
between the radiofrequency pulses (long repetition time) and a long (>
80ms) interval between the radiofrequency pulse and the echo (echo time).
FLAIR sequencing produces heavily T2-weighted images with the CSF-nulled
(1). In the article we did not expect the BMJ readership to be able to
distinguish between FLAIR, STIR or other sequences but rather to
understand the fundamental principles which is the basic MRI dichotomy of
T1 and T2 weighting. This is why the weighting of the image was given in
question and the readers were not left to deduce this for themselves.
Admittedly a more challenging version of quiz could be targeted
specifically for radiologists where the images themselves are displayed
and the interrogatee is expected to determine the image weighting,
sequence and findings. We sought however to target the quiz to a wider
audience.
You correctly point out that most patients with intracranial hypotension
develop cystic hygromas rather than subdural haematomas. We never suggest
otherwise in our article. The subdural collections were subdural
haematomas and were labelled as such. They were not subdural hygromas as
these have same signal intensity as CSF on T2 weighted FLAIR sequence
imaging. We do not feel that the term “subdural effusion” is of any
benefit.
Pachymeningeal enhancement is indeed a feature of spontaneous intracranial
hypotension. This is clearly mentioned in the article. This is most
evident following gadolinium enhancement an agent which was not used in
our patient (2).
We are uncertain how Koumellis and co-workers can surmise that most
radiologists would not describe the sagittal sinus as engorged. For our
part the tense circular cross-section is consistent with engorgement. Our
description is also consonant with that of other authors in the literature
(2). Sometimes this is not apparent until comparison is made with post-
treatment images (2).
Downward displacement of more than 5mm of the cerebellar tonsils is
required for the definition of Chiari malformation and not for absolute
descent of the brainstem (3). Where there is descent of less than 5mm
descent is still recognised and termed cerebellar ectopia (3). The bottom
of the foramen magnum is determined by drawing a line from the most
inferior element of the tip of the clivus (basion) to the most inferior
portion of the foramen magnum (opisthion) (McRae’s line)(3, 4). If such a
line is draw in figure 2 it is apparent that there modest but appreciable
protrusion of the cerebellar tonsils.
Well conducted systematic reviews suggest that CT myelography remains the
investigation of choice to diagnose spontaneous CSF leak (2). This is not
to say that MRI imaging can never be effective as a diagnostic tool.
However its ascendancy over CT myelography can not be based on the single
case report cited (5). Part of the problems lays in the fact that there
exists no definitive guidance from an authoratitive body nor clinical
consensus material on the diagnosis and management of spontaneous
intracranial hypotension. This is part of the reason we presented this
informative article. We hope it has increased the knowledge of the BMJ’s
readership in this important but rare condition.
We thank Koumellis and co-workers for their communication.
1. Ryberg JN, Hammond CA, Grimm RC, et al. Initial clinical
experience in MR imaging of the brain with a fast fluid-attenuated
inversion recovery pulse sequence. Radiology. 1994;193:173-180.
2. Schievink WI. Spontaneous spinal cerebrospinal fluid leaks and
intracranial hypotension. JAMA 2006;295:2284-96
3. Symptomatic tonsillar ectopia. Furuya K, Sano K, Segawa H, Ide K,
Yoneyama H. J Neurol Neurosurg Psychiatry. 1998; 64:221-6.
4. Ishikawa M, Kikuchi H, Fujisawa I, et al. Tonsillar herniation on
magnetic resonance imaging. Neurosurgery 1988;22:77–81.
5. Liong WC, Constantinescu CS, Jaspan T Intrathecal gadolinium-
enhanced magnetic resonance myelography in the detection of CSF leak.
Neurology. 2006 Oct 24;67(8):1522
Competing interests:
None declared
Competing interests: No competing interests