Spontaneous intracranial hypotension (SIH) due to a spinal cerebrospinal fluid leak is a rare but increasing cause of postural headache. Its extravasated epidural fluid collection tends to be non-enhanced or mildly enhanced on enhanced magnetic resonance (MR) imaging. The mild enhancement of the epidural fluid in SIH is usually attributed to fenestrated neovascularization provoked by an inflammatory component, such as blood, of the fluid collection. In this report, we present a case of SIH with a prominent delayed enhancement of the spinal epidural fluid collection on MR imaging. Subsequent vertebral angiography revealed that this delayed enhancement was related to contrast extravasation from a torn anterior meningeal branch of the right vertebral artery. Therefore, we suggest that contrast extravasation from a torn meningeal vessel may be a possible cause of the enhancement in the spinal epidural fluid of SIH.
(Chang Gung Med J 2002;25:854-9)
Keywords：
spontaneous intracranial hypotension, disc herniation, contrast enhancement, magnetic resonance imaging.

Spontaneous intracranial hypotension (SIH) due to a spinal cerebrospinal fluid (CSF) leak is a rare but increasingly recognized cause of postural headaches.(1-14) The spinal CSF leak may extend along a nerve root lateral to the spinal canal or collect within the epidural space of the spinal canal.(6-9) On magnetic resonance (MR) imaging, the epidural fluid collections tend to be non-enhanced or mildly enhanced after gadolinium administration.(7,9) We present an unusual case of SIH with delayed strong gadolinium enhancement in the epidural fluid collection. The subsequent vertebral angiography revealed tears at the anterior meningeal branch of the right vertebral artery. The mechanisms of the abnormal enhancement and arterial tears are discussed.
CASE REPORT

A 46-year-old woman experienced an abrupt onset of severe occipito-cervical and upper back pain while eating dinner. The pain aggravated while standing and alleviated while lying flat. Tracing her medical history, she had bronchiectasis with regular treatment for 6 years, but vigorous cough with blood-tinged sputum occurred unremittingly.
Physical and neurological examinations were unremarkable. The neck was supple. Cerebrospinal fluid examination revealed an opening pressure of 0 mm H2O. A little amount of reddish CSF was drained out on coughing. No CSF analysis was done because of inadequate amount of the sample. Magnetic resonance (MR) imaging of the brain revealed characteristic findings of SIH, including small, bilateral subdural fluid collections, diffuse pachymeningeal enhancement, and prominent dural sinuses (Fig. 1). Spinal MR imaging showed multiple disc herniations, collapsed thecal sac, prominent epidural venous plexus, and diffuse pachymeningeal enhancement. A ventral epidural fluid collection, isointense to CSF on all sequences was noted at the cervicothoracic junction. This fluid collection was mildly enhanced on the initial cervical study, but homogeneously and strongly enhanced 10 minutes after administration of contrast material (Fig. 2). To investigate the unusual enhancement, angiography was performed. On common carotid injections, no obvious abnormalities were seen, but on the right vertebral injection there were tiny spots of contrast leaking from the anterior meningeal branch (Fig. 3). Repeated vertebral angiograms obtained 5 days later showed a decrease of the contrast leakage. Therefore, no neurosurgical intervention was planned and the patient was treated with bed rest and analgesics. One week later, patient's symptoms had improved. A follow-up MR imaging showed resolution of the spinal epidural CSF collection and cerebral and spinal pachymeningeal enhancement (Figs. 1 and 4).

DISCUSSION

Postural headache associated with low CSF pressure is a common clinical syndrome following lumbar puncture. In 1938, Schaltenbrand(1) described a spontaneous form of this syndrome and called it "aliquorrhea". Recently, it has been termed as spontaneous intracranial hypotension and thought to be caused by the rupture of an arachnoid membrane in the spine that allows egress of CSF into the subdural and epidural spaces.(2,8) The imaging findings related to SIH reflect the decreased CSF volume throughout the brain and spine. On computed tomography (CT) of the brain, the findings are usually unremarkable. However, on brain MR imaging, diffuse dural enhancement, prominent dural sinuses, enlarged epidural venous plexus, enlarged pituitary glands, subdural effusions or hematomas, and downward displacement of the cerebral structures are revealed.(2,3,6) Most of the spinal findings of SIH have been studies of radionuclide cisternography and CT myelography.(2,3,8) There have been only a few reports mentioning the associated spinal MR findings.(7,9) Among these findings, collapsed thecal sac and epidural fluid collections are important findings. The spinal epidural fluid collection is believed to be caused by CSF leakage and accumulation.(7) After administration of contrast material, the epidural fluid collection is usually not enhanced or only mildly enhanced.(7,9) Rabin et al(7) attributed the mild epidural fluid enhancement to leakage of contrast material into the collection because of fenestrated neovascularization provoked by an inflammatory component, such as blood, of the fluid collection. In the present case, we saw another cause of enhancement - the contrast extravasation from a torn meningeal vessel.
Reviewing the MR imaging of this case, a herniated disc was seen abutting upon the location of the torn meningeal artery (Fig. 4). A scenario for the arterial tear may begin with a typical disc herniation perforating the complex of the posterior annulus and posterior longitudinal ligament. A focal chemical inflammatory reaction leads to adhesions between the complex and the ventral dural membrane. The tiny meningeal vessels within the adhesive dura may be susceptible to rupture after minor external force, such as cough or retraction force of the collapsed thecal sac owing to SIH. If a tiny vascular tear occurs, the extravasated contrast agent may disseminate slowly into the epidural space. Therefore, we can see epidural enhancement on the delayed study.
For a dural leak of SIH, the treatment options are similar to those for post-puncture headache, including bed rest, analgesics, sedatives, oral caffeine, and intravenous hydration.(2,4) For most patients, the symptoms will resolve over a period of weeks to months.(2,4) More aggressive treatments such as epidural blood patches, saline infusions or neurosurgical interventions may be necessary when the headache persists or is incapacitating.(2,6-8) However, in the literature there has been no mention about the treatment of SIH associated with a torn meningeal vessel. Thus, the question of whether the patients need aggressive treatment arises. According to the angiographic follow-up and clinical course of our case, conservative treatment is suggested first because the injured vessel can heal gradually. Invasive intervention may be reserved until the symptoms become worse.
In conclusion, there have been only few reports on SIH that mentioned the associated spinal MR findings as well as the epidural fluid enhancement.(7,9) However, the enhancement of the epidural fluid was usually attributed to fenestrated neovascularization provoked by an inflammatory component, such as blood, of the fluid collection. In our case, we presented another cause for the enhancement - the contrast extravasation from a torn meningeal vessel.

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From the 2nd Department of Diagnostic Radiology, 1the 2nd Department of Neurology, Chang Gung Memorial Hospital, Taoyuan; Chang Gung University, Taoyuan, Taiwan, R.O.C.
Received: Nov. 13, 2001; Accepted: Mar. 6, 2002
Address for reprints: Dr. Chi-Jen Chen, 2nd Department of Diagnostic Radiology, Chang Gung Memorial Hospital. 5, Fu-Shin Street, Kweishan, Taoyuan 333, Taiwan, R.O.C. Tel.: 886-3-3281200 ext. 3786; Fax: 886-2-27544937; E-mail:radcjc@cgmh.org.tw