Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

: 2012  |  Volume : 22  |  Issue : 2  |  Page : 108--115

Case Series: Long segment extra-arachnoid fluid collections: Role of dynamic CT myelography in diagnosis and treatment planning

Shehanaz Ellika, Horia Marin, Mitchell Pace, Daniel Newman, Muwaffak Abdulhak, Maximilian Kole 
 Department of Radiology, Henry Ford Health System, Detroit, MI, USA

Correspondence Address:
Horia Marin
Division of Neuroradiology, Department of Radiology, Henry Ford Health Systems, 2799 West Grand Blvd, Detroit, 48202. MI


We report five patients in whom spinal MRI revealed extra-arachnoid fluid collections. These spinal fluid collections most likely resulted from accumulation of cerebrospinal fluid (CSF) from a dural leak. The patients presented with either compressive myelopathy due to the cyst or superficial siderosis (SS). All of these fluid collections were long segment, and MRI demonstrated the fluid collections but not the exact site of leak. Dynamic CT myelogram demonstrated the site of leak and helped in the management of these complicated cases. Moreover, we also found that the epicenter of the fluid collection on MRI was different from the location of the leak on a dynamic CT myelogram. Knowledge of these associations can be helpful when selecting the imaging studies to facilitate diagnosis and treatment.

How to cite this article:
Ellika S, Marin H, Pace M, Newman D, Abdulhak M, Kole M. Case Series: Long segment extra-arachnoid fluid collections: Role of dynamic CT myelography in diagnosis and treatment planning.Indian J Radiol Imaging 2012;22:108-115

How to cite this URL:
Ellika S, Marin H, Pace M, Newman D, Abdulhak M, Kole M. Case Series: Long segment extra-arachnoid fluid collections: Role of dynamic CT myelography in diagnosis and treatment planning. Indian J Radiol Imaging [serial online] 2012 [cited 2020 Sep 20 ];22:108-115
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Full Text


Spinal extra-arachnoid fluid collections most likely result from accumulation of cerebrospinal fluid (CSF) due to a dural leak. In most patients, the site of leak can be localized using conventional myelography with delayed CT imaging. However, in some patients with spinal CSF leaks and long spinal fluid collections, there are multiple leaks or large dural tears and the time delay during transfer between myelography and CT scan allows the extrathecal contrast to spread over multiple levels, thus making identification of their source impossible. [1] MRI in all our cases demonstrated the spinal fluid collections but not the exact site of leak. Our study demonstrates the utility of dynamic CT myelogram in identifying the site of leak and its role in the management of these complicated cases.

 Case Reports

Case 1

A 56-year-old presented with a two-year history of progressive bilateral weakness, incoordination of the lower extremities, and progressive hearing loss. Physical examination revealed bilateral lower limb dysmetria, with exaggerated lower limb deep tendon reflexes and Babinski sign bilaterally. He had decreased vibration sensation and proprioception in the lower extremities, walked with a wide-based gait, and had a positive Romberg test. In addition, he had bilateral asymmetric high-frequency sensorineural hearing loss. Cerebrospinal fluid (CSF) and cytological analyses revealed xanthochromia and hemosiderin-laden macrophages.

Typical findings of superficial siderosis (SS) were seen in the brain [Figure 1]A and the spinal cord on MRI. There was long-segment spinal cord T2 signal abnormality, which extended from the medulla to the D 2 spinal segment, with no cord expansion [Figure 1]B. Also noted was a long-segment, nonenhancing, extra-arachnoid fluid collection along the ventral aspect of the thecal sac, extending from C 6 to the D 12 spinal levels, with minimal mass effect on the thecal sac [Figure 1]B. On contrast-enhanced scans there was no abnormal intramedullary enhancement, but vascular enhancement was seen along the anterior and posterior aspects of the cord and lower brainstem, in the midline. The patient subsequently underwent two brain and spine angiograms for the abnormal vascular enhancement seen on the MRI and suspicion of spinal dural arteriovenous fistula, but the investigations were normal.{Figure 1}

Dynamic CT myelography was performed, which also showed the ventral extra arachnoid fluid collection, indicating communication between the collection and the thecal sac. There was similar contrast density in the ventral fluid collection and the thecal sac at the C 5- C 6 level on the immediate dynamic CT myelogram, suggesting site of leak [Figure 1]C and D. The patient was managed conservatively with steroids, and follow-up MRI and repeat dynamic myelography done 1 year later showed spontaneous resolution of the ventral extra arachnoid fluid collection with persistent superficial siderosis. Patient had persistent ataxia, hearing loss and myelopathy which were presumed to be due to superficial siderosis.

Case 2

A 70-year-old male reported with imbalance, ascending numbness and tingling in the lower extremities and progressive hearing loss since 1 year. Sensory exam demonstrated decreased vibration sense in the hands and feet, with decreased perception of pinprick and cold sensation below the ankle. Hoffmann and Babinski signs were present bilaterally. MRI of the brain and spine demonstrated the typical findings of SS in the brain [Figure 2]A-D and spinal cord [Figure 2]E and F. No abnormal flow voids were noted on the brain and spine MRI to suggest an arteriovenous malformation. Also demonstrated was a nonenhancing, extra-arachnoid, ventral fluid collection extending from C 2 to D 9 causing minimal indentation of the anterior thecal sac [Figure 2]E and F. Dynamic CT myelogram was done, which identified a communication between the thecal sac and the ventral fluid collection at the D 1 level [Figure 2]G and H. At surgery, there was a communication between the ventral fluid collection and the thecal sac on the right side above the right D 1 pedicle, with multiple abnormal blood vessels in the right D 1 nerve root sleeve. One of them was potentially the source of the bleeding responsible for the SS and was surgically clipped and the CSF leak was repaired. After surgery, patient developed postoperative complications with pseudomeningocole formation which required re-exploration. After the second surgery patient had stable symptoms of superficial siderosis with improvement of upper extremity signs.{Figure 2}

Case 3

A 58-year-old lady presented with history of a motor vehicle accident followed by a 10-year history of progressive painless wasting and weakness of the left upper extremity. On examination, there was decreased bulk in the intrinsic hand and distal forearm muscles on the left. Hoffman sign and finger flexor jerk were absent on the left. MRI of the spine showed an extra-arachnoid fluid collection extending anteriorlyfrom C 6 to D 1 spinal level, with mild indentation of the thecal sac; the fluid was seen tracking to the left posterolateral epidural space from C 7 to the D 2 levels and becoming ventral in the upper to mid thoracic spine [Figure 3]A-D. Cord T2 signal changes were noted from C 4 to D 1 along with cord atrophy [Figure 3]A-D. A dynamic immediate CT myelogram in the left lateral decubitus showed differential opacification between the thecal sac and the collection [Figure 3]E and communication between the fluid collection and thecal sac, with asymmetric accumulation of contrast in the left C 8 perineural sheath, suggestive of a traumatic pseudomeningocele [Figure 3]F. On the delayed images there was progressively increasing accumulation of contrast within the fluid collection, with homogenous contrast opacification [Figure 3]G. Given the lack of significant cord compression, surgery was not offered to the patient. {Figure 3}

Follow MRI showed spontaneous improvement in the size of the fluid collection with stable weakness in the left upper extremity.

Case 4

A 22-year-old man presented with history of a motor vehicle crash and was evaluated for complaints of neck pain with tingling and numbness in both the upper extremities immediately after the crash, with progression over the next two weeks. His examination revealed brisk tendon reflexes in the upper extremities, with a positive Hoffman test bilaterally. Spinal MRI showed a long-segment, nonenhancing, ventral extra-arachnoid fluid collection extending from C 2 to L 3 [Figure 4]A-D. The thecal sac and cervical cord were displaced posteriorly by this fluid collection [Figure 4]A-D. A dynamic immediate CT myelogram showed equal contrast density in the thecal sac and the ventral fluid collection at the C3-C4 and C 4 -C 5 levels [Figure 4]E and F, suggesting the site of leak with differential opacification below the level of leak [Figure 4]G and H. In addition, there were pseudomeningoceles involving the left C 6 , C 7 , and C 8 nerve roots [Figure 4]I-L.{Figure 4}

A C 5 -C 7 laminectomy was done and the ventral fluid collection was aspirated, followed by closure of the dura in a watertight fashion. The leak could not be identified intraoperatively. A follow-up MRI 6 months later showed persistence of the ventral fluid collections with worsening of symptoms. Patient subsequently had a second surgery with placement of cysto-subarachnoid drainage catheter, which was followed by significant clinical improvement.

Case 5

A 36-year-old man presented with a 3-year history of progressive weakness of his hands-left more than right. At 19 years of age he had suffered a stab injury to the base of the neck on the right and had developed right leg weakness that had progressively improved over the next few months and returned to baseline. On examination, there was decreased bulk in the left forearm, with minimally increased tone in the right upper and right lower extremities. There was significant weakness in the left first dorsal interosseous muscles, with diminished left handgrip. He had slightly reduced vibration sense up to the level of the ankle bilaterally, slightly worse on the left side. There was bilateral sustained clonus and bilateral Hoffman sign. Spinal MRI revealed a focal area of cystic myelomalacia within the right hemicord at the D 1 -D 2 level, with focal right posterolateral tethering of the cord [Figure 5]A-C. A ventral extra-arachnoid fluid collection was seen extending from C 5 through L 2 levels [Figure 5]A-C. Dynamic immediate CT myelogram demonstrated a small area of triangular contrast extravasation along the right posterolateral aspect of the thecal sac at the D 1 -D 2 level and an unopacified ventral fluid collection [Figure 5]D-F. Delayed CT myelogram showed a left posterolateral fluid collection, with differential opacification of the thoracic ventral fluid collection [Figure 5]G-J. At surgery, the right posterolateral leak was identified and repaired. Follow up MRI demonstrated stable ventral fluid collections with clinical improvement of the left upper extremity weakness.{Figure 5}


Spinal extra-arachnoid fluid collections are CSF-filled cavities located within the spinal canal and outside the thecal sac. These fluid-filled cavities have been variably referred to as meningoceles, pseudomeningoceles, diverticula, epidural cyst, or simply as 'fluid collections.' [2] These spinal extra-arachnoid fluid collections are caused by extradural CSF leaks which can be spontaneous, caused by traumatic or iatrogenic (during surgery) dural injury or traumatic avulsion of the brachial plexus. [3],[4],[5],[6],[7] This theory is supported by the observed communication between the extradural spinal collection and the thecal sac seen at dynamic CT myelography in our patients and also noted by several authors. [7],[8],[9],[10] Differential diagnosis for these spinal collections include extradural arachnoid cysts.

Spinal extra-arachnoid fluid collections may present with symptoms related to compressive myelopathy from the collection, SS, or intracranial hypotension. The pathogenesis is usually considered to be an occult CSF leak through small defects in the meninges. Pulsatile CSF dynamics, [11] presence of an osmotic gradient between the subarachnoid space and cyst, [12] and valve-like mechanism between the fluid collection and subarachnoid space [13] may play important roles in the enlargement of these spinal extra-arachnoid fluid collections, which can then cause cord compression and cord signal changes.

In patients with spinal fluid collections, it essential to not only demonstrate the leak but also the site and morphology, because treatment strategy differs dependent on these characteristics. The goal of imaging is to diagnose the extra-arachnoid fluid collections and pseudomeningoceles and also, specifically, to identify the dural defect; this is best characterized by MRI, MR myelography CT myelography,and digital subtraction myelography. [2],[14],[15],[16]

All our cases demonstrated long-segment nonenhancing extra-arachnoid spinal fluid collections that were isointense to CSF on T1W and T2W images. Spinal MRI demonstrated the spinal fluid collections but did not demonstrate the actual site of CSF leak.

In most patients, the site of leak can be localized by using conventional myelography, with delayed CT scans for slower leaks. However, when there are multiple leaks or large dural tears, the time delay during transfer between the myelographic portion of the examination and CT scan allows the extrathecal contrast to spread over multiple levels, thus limiting the ability to localize the leaks. [1] The exact site of dural defect in intraspinal collections spanning long segments can be accurately localized with dynamic CT myelography, [16],[17] which was first introduced for localizing high-flow CSF leaks. [1]

The technique of dynamic CT myelography involves CT acquisition during the initial introduction of the myelographic contrast media into the thecal sac. Specifically, our technique involves puncturing the thecal sac in the lumbar region on the CT Table with the patient in the prone position. A short-segment CT scan over the lumbar segments confirms accurate intrathecal positioning of the needle (scanning the entire spine before injection of contrast is usually not necessary and also increases the radiation dose of the examination). After injection of 10-15 ml of myelographic contrast media, the patient is mobilized to displace the contrast into the spinal segment of interest, e.g., by having the patient adopt a Trendelenburg position to displace the contrast column into the thoracic and cervical spine. The immediate CT acquisition is obtained with the collection in the dependent position. A second delayed acquisition can be obtained after asking the patient to rotate 360°.

Dynamic CT myelogram in all of our cases showed contrast opacification of the extra-arachnoid fluid collection, confirming free communication with the subarachnoid space. Early dynamic CT myelography demonstrated the site of leak where there was similar contrast density within the thecal sac and the fluid collections. All patients had long-segment extra-arachnoid fluid collections, with the epicenter of the collection at a site different from the site of the dural leak.

We understand that dynamic CT myelography is more invasive, has higher radiation dose and is more time intensive. We thus, do not advocate routine use of this technique for all patients with spinal fluid collections. [1] We reserve this technique for a subset of patients with long segment spinal fluid collections with presumed high-flow spinal CSF leaks.

Spinal extra-arachnoid pseudomeningoceles are rare and can be an unrecognized source of chronic bleeding into the subarachnoid space, leading to SS. [18] SS occurs due to chronic or repeated slow hemorrhage into the subarachnoid space that leads to hemosiderin deposition over the cerebral and spinal leptomeninges. [19] Etiologies for SS include root avulsions, tumors, vascular malformations, and brain or spine surgery. [20] In a 1995 survey of the reported SS cases in the literature, a dural pathology was found in 47% of cases. [20] This included CSF cavity lesions (e.g., meningoceles, pseudomeningoceles, pseudoencephaloceles, cavity remaining after a hemispherectomy, and chronic suboccipital hematomas), or root pathology (e.g., root avulsions or epidural cysts). [20] Brachial plexus injury with associated nerve root avulsion is also a common association. [17],[21],[22],[23],[24]

The association of a spinal fluid collection that communicates with the subarachnoid space in patients with SS and history of trauma has been recently been recognized by Kumar et al., [16] and the authors stress the importance of looking for such a communication using dynamic CT-myelogram. In our series, two patients presented with SS, and in one of them extensive brain and spine angiograms did not reveal spinal arteriovenous malformations. It is important to remember that in patients with SS with long-segment extra-arachnoid fluid collections, the bleeding source is usually in the spine, and dynamic CT myelogram helps to locate the exact site of the leak, which then helps in surgical planning.


Our cases illustrate a complex, poorly understood, and difficult-to-clinically-manage entity, which on imaging is represented by extra-arachnoid fluid collections related to occult dural tear and CSF leak. The exact location of the leak is best identified using dynamic CT myelography, and accurate localization helps in planning surgical treatment.


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