Spontaneous Spinal Cerebrospinal Fluid Leaks: A Review

, Cedars-Sinai Neurosurgical Institute, Los Angeles, and Department of Neurosurgery, University of California, Irvine, California

Neurosurg Focus. 2000;9(1) 

In This Article

Diagnosis

Pachymeningeal Enhancement. Magnetic resonance imaging has revolutionized our understanding of intracranial hypotension and undoubtedly is one of the most important factors responsible for the ever-increasing number of patients in whom spontaneous intracranial hypotension can be diagnosed. Enhancement of the pachymeninges (that is, dura mater) following administration of gadolinium is the most characteristic neuroimaging feature of intracranial hypotension (Figs. 2 and 3).[2,8,21,25,28,29,45,49,56,63,64,70,84] This association was first reported in 1991 by Mokri and colleagues.[47] The pachymeningeal enhancement is diffuse, thin, involves both supra- and infratentorial compartments, and may extend into the spinal canal.[44] There has been debate as to the cause of the pachymeningeal enhancement observed on MR imaging. However, careful examination of meningeal biopsy samples consistently demonstrate a thin layer of fibroblasts in the so-called subdural zone as well as small thin-walled dilated blood vessels without evidence of inflammation.[48] Meningeal fibrosis is seen only in patients with long-standing symptoms.[48] These findings strongly suggest that dural venous dilation is the most likely explanation of the pachymeningeal enhancement in intracranial hypotension. Similarly, reactive hyperemia of the pituitary gland in patients with spontaneous intracranial hypotension may mimic a pituitary tumor.[1,45,78]

Figure 2. Axial gadolinium-enhanced T1-weighted MR image demonstrating diffuse pachymeningeal enhancement (arrows) in a 54-year-old woman with a spontaneous CSF leak at the cervicothoracic junction. Note the absence of any leptomeningeal involvement.

Figure 3. Left: Coronal gadolinium-enhanced T1-weighted MR image revealing diffuse pachymeningeal enhancement (curved arrows) and bowing of the optic chiasm over the pituitary fossa (straight arrow) preoperatively (left). Right: Coronal image demonstrating resolution of the pachymeningeal enhancement and restoration of the crowding of the optic chiasm after surgical ligation of a leaking meningeal diverticulum of the left L-2 nerve root in a 41-year-old man.

The presence of pachymeningeal enhancement on MR imaging has been considered to be the sine qua non of intracranial hypotension, and this neuroimaging finding has been believed to be so characteristic that the term "syndrome of orthostatic headache and diffuse pachymeningeal gadolinium enhancement" has been proposed.[49] However, a small minority of patients never develop any meningeal enhancement as seen on MR imaging despite the presence of symptomatic intracranial hypotension.[46,53,76]

Brain Sagging and Pseudo-Chiari Malformation. Downward displacement of the brain, or brain sagging, is a very specific finding in cases of intracranial hypotension. It was first described in 1975 in a patient with spontaneous intracranial hypotension revealed on a pneumoencephalogram.[7] Brain sagging can be identified by several features: effacement of the suprasellar cistern, bowing of the optic chiasm over the pituitary fossa, flattening of the pons against the clivus and obliteration of the prepontine cistern, and hindbrain herniation in which downward displacement of the cerebellar tonsils occurs. (Figs. 3-5).[21,25,29,32,45,56,63,70] Most of these changes are best visualized on the midline sagittal MR images. The displacement of the cerebellar tonsils into the spinal canal may be mistaken for a Chiari I malformation, and some patients with spontaneous intracranial hypotension have undergone decompressive posterior fossa surgery.[70]

Figure 4. Sagittal T1-weighted MR images representative of brain sagging and pseudo-Chiari malformation. Left: A T1-weighted image revealing inferior displacement of the optic chiasm (arrowhead) and severe flattening of the pons (straight arrow) in a 68-year-old man in whom a spontaneous CSF leak was demonstrated at the lumbosacral junction. Center: Image demonstrating inferior displacement of the optic chiasm (arrowhead), mild flattening of the pons (straight arrow), and cerebellar tonsillar herniation mimicking a Chiari I malformation (curved arrow) in a 40-year-old woman with a spontaneous CSF leak at the C-7 level. Right: For comparison, a sagittal T1-weighted image obtained in a healthy 38-year-old woman.

Figure 5. Coronal T1-weighted MR image revealing a subacute left-sided subdural hematoma (straight arrow) and cerebellar tonsillar herniation (curved arrow) in a 42-year-old woman with a spontaneous CSF leak at the C-5 level.

Subdural Fluid Collections. Subdural hematomas and hygromas are commonly found in patients with spontaneous intracranial hypotension (Fig. 5).[2,8,9,21,22,25,29,36,49,51,56,62,63,65,66,70] Most of these subdural fluid collections are bilateral, thin, and do not cause any appreciable mass effect. Occasionally, larger symptomatic subdural hematomas require surgical evacuation, and if the spinal CSF leak is left untreated, the recurrence rate of the subdural hematoma may be increased.[51,65,66] It has been postulated that the subdural hematomas are caused by tearing of bridging veins resulting from the downward displacement of the brain. Alternatively, subdural hematomas may be caused by the rupture of the dilated thin-walled vessels in the subdural zone. The subdural hygromas may represent a compensatory increase of the subdural CSF spaces due to the downward displacement of the brain.

After successful treatment of the underlying CSF leak, improvement or resolution of the MR-documented abnormalities can be expected within several days or weeks (Fig. 3). Clinical improvement generally precedes that demonstrated on neuroimaging. In some patients, particularly those who have not received specific treatment for their CSF leak, considerable clinical improvement is shown over time whereas their MR-documented abnormalities persist.[8,79] In most patients, the pachymeningeal enhancement is the first abnormality that resolves, whereas the brain sagging may linger for a considerably longer time or show only partial improvement.[56,71]

In current practice when the clinical history, physical examination, and imaging studies all are typical of spontaneous intracranial hypotension, additional evaluation may not always be necessary, and the diagnosis can be made with confidence. Prior to the recognition of the characteristic cranial MR imaging findings, a lumbar puncture was the study of choice with which to confirm a diagnosis of intracranial hypotension. With the patient in the lateral recumbent position, normal opening pressure ranges from 65 to 195 mm H2O (5-15 mm Hg) at the level of the lumbar spine.[39] In patients with intracranial hypotension an opening pressure of less than 60 mm H2O is characteristically demonstrated.[62] Not infrequently, a "dry tap" is initially encountered, and CSF can only be obtained with a Valsalva maneuver, placing the patient in an upright position, or with aspiration by using a syringe. A sucking noise has also been described as the stylet is withdrawn and air enters the subarachnoid space, indicating subatmospheric pressure.[4,38,67] It is now well recognized that in some patients with spontaneous spinal CSF leaks and intracranial hypotension who undergo serial lumbar puncture studies, variable readings of CSF pressure are demonstrated over time, including pressures well within the range of normal.[49,70] This may indicate that the CSF leak is intermittent. Normal opening pressures are rarely consistently found in patients with well-documented spontaneous intracranial hypotension.[49] Possibly these opening pressures are subnormal for these patients and their normal CSF pressure is at a higher range. Alternatively, normal, fully compensated CSF pressures may be found in these patients despite reduced CSF volumes.

Examination of a CSF sample often demonstrates abnormal findings.[49,62] An elevated protein content (45 mg/dl) is the most common abnormality and is present in more than three fourths of patients with intracranial hypotension. The increase usually is mild but may reach 1000 mg/dl. Pleocytosis (five white cells/mm3) is found in approximately half of patients. The pleocytosis is primarily lymphocytic and may exceed 200 white cells per mm.[77] Xanthochromia also has been reported. All these CSF abnormalities may be explained by a combination of increased permeability of the dilated meningeal blood vessels and a decrease of CSF flow in the lumbar subarachnoid space.

The fear of cerebral herniation or aggravating symptoms by performing a lumbar puncture is entirely theoretical and has never been documented in patients with spontaneous intracranial hypotension. Not only is the dural hole caused by a lumbar puncture relatively small but the CSF pressure is already low.

Myelography with water-soluble contrast followed by CT scanning is the study of choice to confirm a diagnosis of spontaneous spinal CSF leak and accurately define its location (Figs. 6 and 7).[70,71] Ideally, myelography should be performed in conjunction with the initial lumbar puncture. The use of CT myelography will demonstrate the presence of extrathecal contrast or of structural abnormalities responsible for the CSF leak, such as meningeal diverticula. The CSF leak may appear to be diffuse and the exact site difficult to define, or the leak may be very focal along a single nerve root. The majority of spinal CSF leaks are found at the cervicothoracic junction or in the thoracic spine. Occasionally, multiple simultaneous CSF leaks are demonstrated on myelography at different spinal levels.

Figure 6. Lateral thoracolumbar (left) and lumbar (right) myelogram demonstrating a meningeal diverticulum of the left L-2 nerve root (curved arrows) in a 41-year-old man with spontaneous hypotension.

Figure 7. Postmyelography CT scans demonstrating a focal CSF leak along the right T-12 nerve root in a 24-year-old man (left); a meningeal diverticulum of the left L-2 nerve root (asterisk) in a 49-year-old woman (center); and bilateral complex meningeal diverticula at the T6-7 level (asterisk) in a 35-year-old woman (right).

Myelography should be performed with thin-slice CT cuts at each spinal level from the foramen magnum to the sacrum, unless a previous imaging study has indicated the approximate level of the leak. If the initial CT myelogram fails to demonstrate a leak, it may be of benefit to have the patient ambulate for some time and then to obtain a delayed CT scan to identify a slow or intermittent spinal CSF leak. Infusion of artificial CSF following the installation of contrast also may improve the detection rate of spinal CSF leaks by increasing intrathecal pressure.

Radionuclide cisternography with 111 Indium-diethylenetriamine pentaacetic acid has been used extensively in the evaluation of patients with spontaneous intracranial hypotension (Fig. 8).[13,40,50,62,63,70,71,79] In most cases, this study will show early accumulation of tracer in the kidneys and bladder, slow ascent along the spinal axis, and less activity than expected over the cerebral convexities. These findings suggest unusually rapid uptake of tracer into the bloodstream through the extensive epidural venous plexus. However, this diagnostic modality identifies the location of the CSF leak in only about two thirds of patients in whom CT myelography has defined spinal CSF leaks.[70] It is likely that in such cases the CSF leak is below the level of resolution of the radionuclide study. Nevertheless, radionuclide cisternography may be useful to confirm a diagnosis of intracranial hypotension when CT myelography demonstrates normal findings or to aid in the localization of the CSF leak when CT myelography suggests multiple simultaneous spinal CSF leaks.

Figure 8. Radionuclide cisternograms with 111 Indium-diethylene-traimine pentaacetic acid demonstrating spontaneous CSF leaks at the cervicothoracic junction (curved arrows) in a 51-year-old woman (left) and at the left lumbosacral junction (curved arrow) in a 68-year-old man (right).

Spinal MR imaging has played a relatively limited role in the evaluation of patients with spontaneous intracranial hypotension.[43,49,60,62,70] Although extrathecal CSF collections and meningeal diverticula are routinely visualized on MR imaging in patients with spontaneous intracranial hypotension (Fig. 9), often MR imaging is not sensitive enough to detect the exact location of the spinal CSF leak. Magnetic resonance myelography is a novel technique[31,61] that may prove to be valuable in the localization of spinal CSF leaks.[41] Dilated epidural veins are commonly visualized using MR myelography in patients with spinal CSF leaks, and these veins may mimic an arteriovenous malformation or jugular vein thrombosis.[11,43]

Figure 9. Axial T2-weighted MR image revealing bilateral complex meningeal diverticula of the S-1 nerve roots (curved arrows) in a 55-year-old woman with Marfan syndrome.

Transorbital color Doppler flow imaging of the superior ophthalmic veins is a recently described method to diagnose intracranial hypotension.[10] Using this imaging technique, Chen and colleagues[10] have observed high blood flow velocities in greatly engorged superior ophthalmic veins in all their patients with spontaneous intracranial hypotension. Flow velocities returned to normal after successful treatment of the intracranial hypotension.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....