MR images as compared with combined myelography and computed tomography. Key words: Magnetic resonance Spinal cord - Arach- noid cyst. An arachnoid ...
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Case reports
9 Springer-Verlag 1990
Child's Nerv Syst (1990) 6:107-109
Magnetic resonance diagnosis of spinal arachnoid cyst A report of two cases A.Jena 1, R.K. Gupta 1, A. Sharma 2, V.E.D. Prakesh 3, and S. Khushu i t NMR Research Centre, Institute of Nuclear Medicine and Allied Sciences, Lucknow Road, Delhi-110007, India z Department of Neurosurgery, G.B. Pant Hospital, New Delhi-110002, India 3 Neuro Centre, Army Hospital, Delhi Cantt, India Received March 17, 1989
Abstract. M a g n e t i c r e s o n a n c e ( M R ) findings in one case each o f e x t r a d u r a l a n d i n t r a d u r a l a r a c h n o i d cyst are described. T h o r a c i c segments were i n v o l v e d in b o t h cases. T h e cysts were slightly m o r e intense t h a n c e r e b r o s p i n a l fluid in b o t h cases o n T1 weighted images. T h e n a t u r e a n d extent of the lesions were better d e m o n s t r a t e d o n M R images as c o m p a r e d with c o m b i n e d m y e l o g r a p h y and computed tomography.
Key words: M a g n e t i c r e s o n a n c e
Spinal cord - A r a c h -
n o i d cyst
A n a r a c h n o i d cyst is a n e x p a n d i n g d i v e r t i c u l u m o f the s u b a r a c h n o i d space, which is lined o n l y by a r a c h n o i d a n d u s u a l l y c o m m u n i c a t e s with the s u b a r a c h n o i d space t h r o u g h a relatively n a r r o w neck. Such diverticula m a y r e m a i n c o n f i n e d w i t h i n the i n t r a d u r a l space, m a y herniate t h r o u g h a d u r a l defect into the e x t r a d u r a l space, or m a y have a significant c o m p o n e n t in each of the two spaces [6]. T h e d i a g n o s i s is u s u a l l y established by e n t r y of contrast medium into the cyst either o n m y e l o g r a p h y or o n c o m p u t e d t o m o g r a p h y (CT) m y e l o g r a p h y [ 1 - 4 , 6, 8, 10, 11]. R e c e n t l y the role of m a g n e t i c r e s o n a n c e ( M R ) in the diagnosis o f spinal a r a c h n o i d cysts has been described [9-12]. We p r e s e n t two cases of spinal a r a c h n o i d cysts which did n o t show e n t r y of c o n t r a s t m e d i u m o n myelogr a p h y a n d where the diagnosis was suggested only o n MR.
Case reports Case 1 An 11-year-old boy was admitted with complaints of progressive weakness of both lower limbs for a period of 1 year. He had had no significant illness in the recent past. Physical examination revealed Offprint requests to: A. Jena
spastic paraparesis with exaggerated deep tendon reflexes. Plain radiography of the dorsolumbar spine showed expansion of the spinal canal with posterior scalloping of dorsal vertebral bodies. Myodil myelography was performed and showed complete extradural block at the level of L1 vertebra. Cisternal myelography revealed the upper limit of the block at the D4 vertebra. To assess the nature of the mass lesion, CT was performed and showed an apparently solid mass lesion. MR was performed on a 1.5 Tesla superconducting system (Magnetom, Siemens), using the spin-echo technique. T1 weighted imaging employed a repetition time (TR) of 700 ms and echo time (TE) of 28 ms. T2 weighted images were performed at a TR of 2800 ms with two echoes obtained at a TE of 28 ms for first echoes and 84 ms for the second echo. Slice thickness was 5 mm with no interslice gap. The matrix size was 256 x 512. Imaging was performed in saggital and axial planes. MR showed an extradural lesion, extending form D4 to L1 vertebrae, and measuring 15.0x3.8cm. The mass appeared as slightly more intense than cerebrospinal fluid (CSF) on T1 weighted images and more hyperintense than CSF on T2 weighted images, suggesting the cystic nature of the mass. The cyst was lysing posterior to the spinal cord and was pushing it anteriorly (Fig. I a c). Based on the above MR features, the diagnosis of extradural arachnoid cyst was considered. Laminotomy was performed and the cyst was excised. The contents of the cyst were sent for biochemical analysis and the wall was sent for histological examination. The protein content of the cyst measured 100 mg per deciliter. Histopathology was consistent with the diagnosis of arachnoid cyst.
Case 2 A 17-year-old boy was evaluated for a 4-month history of weakness of both lower limbs and the right upper limb. On physical examination, he had spastic paraparesis and weakness of the right upper limb. The deep tendon reflexes were brisk and Babinski's sign was positive. Sensory changes consisted of hypoalgesia and hyperasthesia from C7 to DI. The patient had been operated for cervical syringomyelia in 1979. Metrizamide myelography was performed and showed an apparently dilated spinal cord at C7 and D2 with evidence of laminectomy. No evidence of any compression of the cord was demonstrated. MR was performed to evaluate the extent of the lesion using the same technique and parameters as described in case 1. A cyst was demonstrated anterolateral to the spinal cord, compressing it posteriorly, suggesting an intradural cyst (Fig. 2 a, b).
108
Fig. 1 a-c. Extradural arachnoid cyst. a Sagittal MR through dorsolumbar spine (SE 700/28) shows low intensity well-defined cyst extending from D4 to L1 lying posterior to spinal cord. The bright areas posterior to the cyst are due to extravasated myodil. Note the higher intensity of the cyst as compared with the CSF. b Sagittal MR (SE 2800/84) shows high intensity signal from the cyst. Note the low intensity signal between spinal cord and cyst, representing the thickened dura mater, e Axial MR through D6 vertebra shows a (SE 700/28) hypointense mass posterior to the spinal cord pushing it anteriorly Fig. 2a, b. Intradural arachnoid cyst. a Sagittal midline MR (SE 700/28) shows low intensity mass anterior to the spinal cord pressing it posteriorly. It lies at C7 and D 1 vertebrae. Note that the
intensity of the cyst is higher than the CSE b T2 weighted sagittal image (SE 2800/84) shows high intensity signal from the cyst
The cyst measured 4.2 x 5.2 cm and was slightly more hyperintense than CSF on TI and T2 weighted images. The diagnosis of intradural arach,noid cyst was considered on MR involving C7-D1 vertebral levels. On operation, an intradural arachnoid cyst was found adherent to the spinal cord and was exised. Histology confirmed the diagnosis of arachnoid cyst. Biochemical examination of the cyst contents revealed 110 mg per deciliter of protein.
The signal characteristics of the cyst contents on the modulus variant of inversion recovery and spin-echo sequences parallel those of CSF and allow a distinction from the protein-containing contents of cystic neoplasms [5]. Kjos et al. described CSF-like (low protein content), intermediate (intermediate protein content), and high intensity (high protein content) patterns in cases of arachnoid cyst, tumoral cyst, and hemorrhagic or colloid cyst respectively [7]. They postulated that the presence of protein macromolecules shortens the T1 value of the fluid, hence alteration of fluid intensity on T1 weighted images in various types of cysts. The arachnoid cysts have been described as isointense with CSF on T1 weighted images [5, 7]. In the present series, both extra- and intradural arachnoid cysts showed slightly higher intensity than CSF and T1 weighted images. The higher protein content in these cysts can be explained by loculation of CSF in the cyst due to poor communication with the subarachnoid space [8]. Higher protein content of both the cysts resulted in slightly higher signal intensity of cysts than CSF on TI weighted images. Intradural arachnoid cysts may occur anywhere along the spinal axis. They are most frequently found in the thoracic region, posterior to the spinal cord [6, 10]. Those lesions in which trauma, surgery, inflammation, or the presence of blood or contrast material in the subarachnoid space are believed to be the causative or con-
Discussion Spinal arachnoid cysts are usually filled on supine myelography [6]. The precise site of communication with the subarachnoid space is less frequently demonstrated [10]. An unfilled cyst m a y simulate any other smooth mass, though the posterior situation is typical of an arachnoid cyst [6]. Arachnoid pouches with the septum posticum, which retain contrast medium but do not compress the spinal cord, are frequently the cause of partial or complete obstruction to the passage of CSF. In the present cases, communication of the arachnoid cyst with the subarachnoid space could not be shown on myelography. Case 2 showed obvious compression of the spinal cord by an anteriorly placed cyst on MR, which was missed altogether on myelogram. Plane CT in case 1 showed higher Hounsfield vah~es of the lesion than CSF, which is consistent with a mass lesion. On MR, the extent, size, and nature of the lesions were well demonstrated.
109 tributory factors are usually classified as acquired [6, 10]. The etiology in the present case 2 was post surgical, the cyst was anterior to the spinal cord, and involved the cervicodorsal region. Cervical intradural a r a c h n o i d cysts have been reported previously and two o f them were anteriorly placed [2]. Extradural a r a c h n o i d cysts are usually large, extending two to six vertebral segments and cause complete block or high-grade obstruction on m y e l o g r a p h y [6, 10]. The d u r a and s u b a r a c h n o i d spaces are usually displaced anteriorly or laterally a w a y f r o m the cyst. The cord m a y be n o r m a l or m a y be displaced and compressed. In the present case the cyst was placed posterior to the spinal cord, displacing it anteriorly, and involved ten vertebral segments. It is concluded that M R should be the m o d a l i t y o f choice in the d e m o n s t r a t i o n o f spinal a r a c h n o i d cysts as it depicts the extent, site, and nature o f the lesion extremely well. A r a c h n o i d cysts p o o r l y c o m m u n i c a t i n g with the s u b a r a c h n o i d space have a higher protein content than n o r m a l C S F and a p p e a r a little hyperintense c o m p a r e d with C S F on T1 weighted images.
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