eMedicine Specialties > Radiology > Brain/Spine

Leptomeningeal Carcinomatosis: Imaging

Author: Andrew L Wagner, MD, Assistant Professor of Radiology, Instructional Faculty, University of Virginia School of Medicine; Director of Neuroradiology, Department of Radiology, Rockingham Memorial Hospital
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Updated: Feb 1, 2007

Computed Tomography

Findings

Contrast-enhanced CT (CECT) scans of the brain in LC are not sensitive in depicting the disease, with a false-negative rate of more than 50%. Common findings include noncommunicating hydrocephalus, intraparenchymal volume loss, and various patterns of meningeal enhancement (see Image 6). This enhancement can appear as multiple nodules, diffuse leptomeningeal enhancement, ependymal or subependymal enhancement, dural enhancement, or a combination. In the nodular form, pial enhancement is difficult to distinguish from intraparenchymal enhancement, although recognizing that the nodules follow the course of sulci assists in the diagnosis.

Cranial nerve enhancement is poorly visualized on CECT because of the proximity to osseous structures. Dural enhancement often is missed for the same reason.

In the spine, CECT also has low sensitivity, although CT myelography is approximately equal in sensitivity to MR in the detection of nerve root thickening and nodularity. The nerve roots appear thickened and beaded, and this is best visualized in the cauda equina. Tumor deposits along the surface of the cord lend the cord an irregular border, and the cord may be thickened. In extreme cases, the entire spinal canal can be filled with tumor, causing a complete CSF block.

Degree of Confidence

As described previously, both CECT and CT myelography compare unfavorably with newer MR imaging and have high false-negative rates. CECT in particular also suffers from poor specificity, as there are other disease processes that cause leptomeningeal enhancement. In the current workup of LC, limit these tests to those patients who cannot undergo an MR examination.

False Positives/Negatives

False-negative CECT scans occur in more than 50% of patients with LC. In some of these, the disease is not detectable on any imaging study, but in others, the limitations of CT imaging result in a missed diagnosis. Potential errors include lower contrast resolution than MR, adjacent dense osseous structures, and beam-hardening artifact, particularly in the posterior fossa.

False positives can be caused by benign meningeal enhancement, such as in patients with dural enhancement following LP or postsurgery and in those with intracranial hypotension. Diffuse benign parenchymal loss can mimic the volume loss and hydrocephalus associated with LC.

Magnetic Resonance Imaging

Findings

• A protocol for evaluation of intracranial leptomeningeal tumor should include postcontrast T1-weighted images in more than one plane. The coronal plane is helpful in the detection of disease over the convexities and in the cerebellum. Thin-section sequences such as magnetization prepared-rapid acquisition gradient echo (MP-RAGE) or spoiled gradient-recalled acquisition in a steady state (SPGR) following contrast are of use when evaluating the cranial nerves, as are precontrast, high-resolution, bright-CSF sequences such as constructive interference in a steady state (CISS). Recently, postcontrast fast FLAIR images have been reported to be even more sensitive to leptomeningeal enhancement than postcontrast T1 sequences (see Images 7-8). However, noncontrast FLAIR, which was thought to be a good imaging sequence for LC, is less sensitive than T1 contrast-enhanced images.
• Leptomeningeal tumor has a spectrum of appearances on MR ranging from diffuse leptomeningeal enhancement to bulky extra-axial tumor foci. The most common appearance is diffuse nonnodular enhancement of the basilar cisterns and/or supratentorial cortex, although this MR appearance is not specific for LC. Hydrocephalus without discernible enhancement also is commonly seen, but the appearance is nonspecific.
• Multiple enhancing leptomeningeal nodules also can be visualized in patients with LC, typically demonstrating larger tumor deposits in the basilar cisterns than in the supratentorial sulci. These nodules may form large clumps of tumor that cause mass effect on the adjacent brain. Even small amounts of tumor may result in obstructive hydrocephalus if they are located in narrow portions of the ventricular system, such as the fourth ventricle and aqueduct of Sylvius. When the tumor deposits are located in the supratentorial sulci, it may be difficult to distinguish them from intraparenchymal metastases, although recognizing that the enhancing nodules follow the course of the deep sulci suggests the correct diagnosis of leptomeningeal disease. Another pattern that has been described as mimicking intraparenchymal spread is nodules within the Virchow-Robin (perivascular) spaces.
• Cranial nerves often are involved clinically in LC, although many of these cases are radiologically occult. High-resolution contrast-enhanced techniques with fat saturation aid in the detection of cranial nerve tumor deposits, but pay close attention to the nerves in many cases to detect the subtle abnormalities. Although multiplanar imaging increases the sensitivity of detecting LC, coronal images best demonstrate the cranial nerves in most patients. Involved cranial nerves may have mild peripheral enhancement, which may be easily missed, as the only MR abnormality. When there is more gross involvement, nerves may be enlarged and irregular, with nodular enhancement, making detection easier. However, without a high index of suspicion, many cases can be missed easily because of the small size of the nerves and their course through the skull base.
• Spinal cord involvement mimics that of the brain stem, with peripheral linear or nodular enhancement of the pia mater. In addition, enhancement of the nerve roots within the cauda equina is often seen, ranging from tiny nodules to large masses. When spinal leptomeningeal disease is caused by direct extension from vertebral body metastases, fat-saturated enhanced T1-weighted images can be used to optimally demonstrate the vertebral body and epidural enhancement.

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. 

NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Degree of Confidence

Although MR is the most sensitive and specific imaging study to evaluate for the presence of leptomeningeal tumor, there are cases where the MR may be negative in the presence of LC diagnosed by lumbar puncture, and a negative MR does not exclude the presence of disease. Gomori et al reported a 12% incidence of positive CSF cytology when in the presence of a negative MR spine examination but also found that MR was positive in 60% of patients with LC with negative CSF cytology. This suggests that the two techniques are complimentary and should not be performed if the initial test is negative.

MR findings in LC are nonspecific, as bacterial or fungal meningitis, leptomeningeal sarcoidosis, recent surgery, and even, on occasion, cerebral infarction may have a similar appearance. The estimated sensitivity of MR in the detection of LC is 34-71%, although this includes all tumor types. Separating LC into two subtypes, Freilich et al found MR abnormalities in 90% of LC from solid tumors and in 55% of patients with hematologic malignancies as the tumor of origin. Another study found even lower sensitivity of MR in hematologic LC, reporting only 6% sensitivity, although this was performed on earlier MR machines.

Another application of MR is evaluation of the presence or absence of CSF flow obstruction. MR flow studies using cardiac-gated phase contrast techniques can be used to display and quantitate cerebrospinal flow in the head and spine, and to evaluate CSF flow obstruction. In addition, spinal cord motion also may be observed to evaluate tethering or compression by metastatic disease. A nuclear medicine CSF flow study also may be performed.

False Positives/Negatives

As previously stated, recent surgery can mimic LC because of postoperative leptomeningeal enhancement. Any procedure involving CSF access, including LP, can result in long-term dural enhancement that can mimic neoplasm.

Normally enhancing vessels on the surface of the cord can be mistaken for leptomeningeal tumor spread if the linearity of the vessel is not appreciated. These are usually venous structures, as the anterior and posterior spinal arteries usually run in the same location relative to the cord. Patients who have undergone radiation therapy to the spine may have dilated vessels that can mimic LC.

Meningitis may also mimic LC, and oncology patients are often predisposed to this secondary to immunosuppression and hospitalization.

Nuclear Imaging

Findings

The nuclear medicine study most commonly ordered in LC is a radioisotope CSF flow study to document the presence or absence of an obstruction to CSF flow in the spine or skull base. Although much less sensitive than MR to the presence of LC, CSF flow studies are considered almost 100% sensitive to the presence of obstructive CSF space disease. The procedure is performed by injecting Indium In 111–labeled diethylenetriamine pentaacetic acid (DTPA) into the CSF through either an LP or an indwelling catheter such as an Ommaya reservoir. Images generally are obtained for 60-90 minutes, and a 24-hour delayed image is frequently obtained.

In his 1998 article, Chamberlain describes the normal time for radioisotope to be seen in the different compartments following both lumbar and intraventricular injections and breaks down the intraventricular injections into adult and pediatric patients.

CSF flow studies are important when considering intrathecal chemotherapy, as in up to 70% of patients with LC some form of CSF flow obstruction exists that will affect the spread of the chemotherapeutic agent, thus its toxic effects and efficacy. Areas that demonstrate an obstruction on a CSF flow study can be treated with external beam radiation prior to intrathecal chemotherapy.

Degree of Confidence

As mentioned above, although the CSF flow study is not as sensitive as MR for the detection of any leptomeningeal tumor, the sensitivity, specificity, and accuracy for detection of CSF flow obstruction is 100%.

False Positives/Negatives

In CSF flow studies performed through a LP, ensure that the injection is within the subarachnoid space, as a subdural or epidural injection mimics a complete obstruction. Confirmation of needle placement using a small amount of contrast avoids this potential error.

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