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Submitted material: Entrust image interpretation to the experts.
- Panos Koumellis, Amlyn L Evans, Robert K Lenthall, Tim Jaspan. (1 April 2009)
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Entrusting Image Interpretation to Radiologists?
- Chika E Uzoigwe, Ali O, Srikantha M, Bhat W (15 April 2009)
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Panos Koumellis, Radiology Registrar Neuroradiology Department, Queen's Medical Centre, Derby Road, Nottingham, NG7 2UH, Amlyn L Evans, Robert K Lenthall, Tim Jaspan.
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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 |
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Chika E Uzoigwe, Speciality Registrar Trauma & Orthopaedics Milton Keynes General Hospital, Ali O, Srikantha M, Bhat W
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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 |
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