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(Radiology. 2000;217:50-53.)
© RSNA, 2000

Neuroradiology

Intracranial Leptomeningeal Metastases: Comparison of Depiction at FLAIR and Contrast-enhanced MR Imaging1

Sanjay K. Singh, MD, Jacob M. Agris, MD, Norman E. Leeds, MD and Lawrence E. Ginsberg, MD

1 From the Department of Diagnostic Radiology, University of Texas M.D. Anderson Cancer Center, Box 57, 1515 Holcombe Blvd, Houston, TX 77030. From the 1999 RSNA scientific assembly. Received December 15, 1999; revision requested January 13, 2000; revision received February 29; accepted March 7. Address correspondence to S.K.S. (e-mail: ssingh@di.mdacc.tmc.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To compare contrast material–enhanced T1-weighted and fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) images in depicting leptomeningeal metastases.

MATERIALS AND METHODS: Malignant lesions detected at cytologic examination of cerebrospinal fluid in 70 patients were reviewed. There were 58 studies in which both FLAIR and contrast-enhanced T1-weighted spin-echo MR images were available. A senior neuroradiologist reviewed the images from each sequence individually and separately for signs of leptomeningeal metastases and assigned a diagnostic rating of positive, indeterminate, or negative.

RESULTS: Leptomeningeal metastases were depicted in 38 cases on contrast-enhanced T1-weighted spin-echo images and in 20 cases on FLAIR images. In three cases, leptomeningeal metastases were detected by using only FLAIR images. In 20 cases, leptomeningeal metastases were detected by using only contrast-enhanced T1-weighted spin-echo images. FLAIR imaging has a sensitivity of 34% for cytologically proved leptomeningeal metastases. Gadolinium-enhanced MR imaging has a sensitivity of 66%.

CONCLUSION: Used alone, contrast-enhanced T1-weighted images are better than FLAIR images for detecting leptomeningeal metastases. This is particularly true for cases in which leptomeningeal metastases manifest primarily or solely as cranial nerve involvement.

Index terms: Brain neoplasms, MR, 139.121411, 139.121413, 139.12143, 159.121411, 159.121413, 159.12143 • Brain neoplasms, secondary, 139.38, 159.38 • Magnetic resonance (MR), comparative studies, 139.121411, 139.121413, 139.12143, 159.121411, 159.121413, 159.12143 • Magnetic resonance (MR), inversion recovery, 139.121413, 159.121413 • Magnetic resonance (MR), pulse sequences, 139.121411, 139.121413, 139.12143, 159.121411, 159.121413, 159.12143 • Meninges, neoplasms, 139.38, 159.38


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging of the brain is known to be sensitive for the detection of parenchymal lesions (1–4). More recently, FLAIR imaging has been shown to be efficacious in the detection of subarachnoid hemorrhage, meningoencephalitis, and leptomeningeal metastases (5–7). It has been suggested that FLAIR images may eliminate the need for contrast material–enhanced T1-weighted spin-echo images in the diagnosis of leptomeningeal disease (5). The purpose of our study was to compare contrast-enhanced T1-weighted and FLAIR MR images in depicting leptomeningeal metastases.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
The routine use of FLAIR sequences in brain imaging at our institution began in November 1997. We searched the cytology database starting from that time through June 1999 for patients with cerebrospinal fluid cytologic examination results positive for malignant cells. This yielded 113 patients. Of these patients, 70 had brain MR imaging studies. All patients had FLAIR and T1-weighted studies that were performed after the administration of contrast material at the same time as part of the brain MR imaging study. The subset of patients who had brain MR studies temporally related to cerebrospinal fluid sampling consisted of 53 patients (28 female and 25 male patients; age range, 4–76 years; mean age, 47 years).

The diagnoses were melanoma (14 patients), breast carcinoma (11 patients), lymphoma (10 patients), leukemia (seven patients), lung carcinoma (five patients), glioblastoma (three patients), astrocytoma (one patient), retinoblastoma (one patient), and unknown primary carcinoma (one patient). The total number of brain MR studies reviewed was 58, as three patients had disease relapse and repeat work-ups, with a total of five additional studies. The MR imaging studies included in this review were performed no more than 14 days prior to the diagnosis of leptomeningeal metastases (53 studies) or within 3 days after the diagnosis (five studies).

MR imaging examinations were performed with 1.5-T systems (Signa Horizon; GE Medical Systems, Milwaukee, Wis). The FLAIR sequences were in the transverse plane with flow compensation and were fast FLAIR sequences: 10,000/147/2,200 (repetition time msec/echo time msec [effective]/inversion time msec) with an echo train length of 22. The bandwidth was 16 kHz, and the matrix was 256 x 160. The T1-weighted images were obtained in all three imaging planes after intravenous injection of gadopentetate dimeglumine (Magnevist; Berlex, Wayne, NJ) at a dose of 0.2 mL per kilogram of body weight. T1-weighted images (600/8 [repetition time msec/echo time msec]) were not obtained with flow compensation. The bandwidth was 16 kHz, and the matrix was 256 x 192. For both sequences, the field of view was 20 cm, with a section thickness of 5 mm and an intersection gap of 1.5 mm.

The transverse FLAIR images were separated from the transverse contrast-enhanced T1-weighted spin-echo images. A senior neuroradiologist (L.E.G.), who was blinded to patient identity but was aware of the malignant cytologic findings in all patients, reviewed transverse FLAIR sequences and assigned a rating of positive, indeterminate, or negative for leptomeningeal metastases for each case. A positive rating was assigned when abnormally high signal intensity was present in the cisterns, ventricles, sulci, or any pial surface.

At a separate session, the same reviewer evaluated the transverse contrast-enhanced T1-weighted images for leptomeningeal metastases. Contrast-enhanced images were evaluated for the presence of abnormal leptomeningeal enhancement in the sulci and cisterns and for abnormal cranial nerve enhancement. Only the transverse T1-weighted contrast-enhanced images were reviewed, but in five cases the coronal T1-weighted contrast-enhanced images were also evaluated to determine if sulcal enhancement on the transverse images represented normal cortical vessels. In reviewing the images, the reader was allowed to rate either FLAIR or contrast-enhanced T1-weighted images as indeterminate if he could not diagnose leptomeningeal metastases confidently and was uncertain whether a finding was truly an artifact or a normal structure.

To analyze the utility of the two sequences, we identified and reevaluated the cases that were positive when images obtained by using one technique were viewed but were negative or indeterminate when the images were obtained by using the other technique. At this time, the transverse FLAIR and transverse contrast-enhanced T1-weighted images were compared side by side to evaluate the location of the abnormalities on the positive images.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
In 58 cases, the FLAIR images were positive in 20, negative in 32, and indeterminate in six (Table 1). In the setting of proved neoplastic leptomeningeal metastases, FLAIR imaging had a sensitivity of 34% (20 of 58). The contrast-enhanced T1-weighted images were positive in 38 cases, negative in 17, and indeterminate in three. This yielded a sensitivity of 66% (38 of 58).


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  		TABLE 1. Results of Reading FLAIR and Postcontrast T1-weighted Images for Leptomeningeal Metastases
 
There were three cases that were positive at FLAIR and negative or indeterminate at contrast-enhanced T1-weighted spin-echo imaging (Table 2). The abnormalities in all three instances were in the cerebral sulci (Fig 1).


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  		TABLE 2. Leptomeningeal Metastases Visible by Means of Only One Technique
 


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  		Figure 1a. Transverse MR images of leptomeningeal metastases in a 31-year-old woman with melanoma. (a) Gadolinium-enhanced T1-weighted MR image (600/8) has no abnormal enhancement. (b) FLAIR image (10,000/147/2,200) demonstrates predominantly left posterior sulcal increased signal intensity (arrowheads).

 


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  		Figure 1b. Transverse MR images of leptomeningeal metastases in a 31-year-old woman with melanoma. (a) Gadolinium-enhanced T1-weighted MR image (600/8) has no abnormal enhancement. (b) FLAIR image (10,000/147/2,200) demonstrates predominantly left posterior sulcal increased signal intensity (arrowheads).

 
Twenty studies were positive at contrast-enhanced T1-weighted spin-echo imaging and negative or indeterminate at FLAIR imaging (Table 2). In seven cases, the abnormalities involved only the cerebral and/or cerebellar sulci. In 12 studies, the findings were located in the cisternal spaces, where predominantly cranial nerves were involved. One case had both types of findings (Fig 2).



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  		Figure 2a. Transverse MR images of leptomeningeal metastases in a 30-year-old woman with lymphoma. (a) Gadolinium-enhanced T1-weighted MR image (600/8) shows enhancement of the fifth cranial nerves (arrowheads) and cerebellar sulci (arrows). (b) FLAIR image (10,000/147/2,200) does not demonstrate definite abnormal signal intensity and was read as negative.

 


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  		Figure 2b. Transverse MR images of leptomeningeal metastases in a 30-year-old woman with lymphoma. (a) Gadolinium-enhanced T1-weighted MR image (600/8) shows enhancement of the fifth cranial nerves (arrowheads) and cerebellar sulci (arrows). (b) FLAIR image (10,000/147/2,200) does not demonstrate definite abnormal signal intensity and was read as negative.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The survival of patients with malignant leptomeningeal metastases is between 1 and 2 months without treatment (8–10). With palliative treatment, survival can be up to 6–10 months (8,10). Early detection of leptomeningeal metastases not only is crucial to overall prognosis but also allows earlier institution of appropriate therapy to preserve neurologic function (8).

Imaging of leptomeningeal metastases is important, since cerebrospinal fluid cytologic examination results are often falsely negative and leptomeningeal metastases occasionally may be asymptomatic and unsuspected clinically. The imaging appearance of leptomeningeal metastases ranges from pial lesions, either diffuse or focal masses, to cisternal lesions attached to either the dura or cranial nerves (11–13). Hydrocephalus is present in some cases (13).

The imaging of leptomeningeal metastases has evolved. MR imaging without intravenously administered contrast material was less sensitive than contrast-enhanced computed tomography (14). The introduction of paramagnetic contrast materials improved the relative sensitivity of MR imaging for leptomeningeal metastases (11). Contrast-enhanced MR imaging became the study of choice for detecting leptomeningeal metastases; however, even contrast-enhanced MR imaging has a reported sensitivity of 71% (15 of 21 [11]) or less (12) for leptomeningeal metastases. This has prompted the search for more sensitive imaging techniques.

The FLAIR sequence has great utility in detecting not only parenchymal lesions (1–4) but also leptomeningeal or subarachnoid abnormalities such as subarachnoid hemorrhage and inflammatory and neoplastic meningitis (5,15). If FLAIR imaging is more sensitive than contrast-enhanced T1-weighted spin-echo imaging for leptomeningeal disease (5), contrast material may not be needed for images obtained specifically for detecting leptomeningeal or subarachnoid disease.

Our data indicate that, at least for leptomeningeal metastases, FLAIR images are not better than contrast-enhanced T1-weighted images. Although there are cases in which FLAIR images depict abnormalities not identified on contrast-enhanced T1-weighted spin-echo images, overall the latter are more sensitive.

Our data are limited in several respects. First, with 100% disease prevalence in the population studied, no information about specificity is available. Second, because the reviewer was aware that all patients had disease, there was an inherent bias toward giving a positive rating. Therefore, in the clinical setting in which patients without leptomeningeal metastases are present, the sensitivity for both FLAIR and contrast-enhanced T1-weighted imaging may be lower. In addition, as only one reviewer was used, no assessment regarding interobserver reliability is available.

Nevertheless, the comparison between the two sequences is revealing; contrast-enhanced T1-weighted images are better in depicting cisternal leptomeningeal lesions, particularly those involving cranial nerves. In part, the reason for this appears to be the artifactually high signal intensity on FLAIR images owing to the motion of cerebrospinal fluid. This limitation of FLAIR images has been noted previously (4,15). This signal intensity is most marked in the cisterns of the posterior fossa (Fig 3) and often is present despite flow compensation. Three-dimensional fast FLAIR imaging theoretically should diminish the cerebrospinal fluid pulsation artifacts because of smaller amounts of unsaturated cerebrospinal fluid entering the imaging volume (16,17). Even when the FLAIR images were not plagued by false signal intensity in the cisterns, abnormalities were much more conspicuous on the contrast-enhanced T1-weighted images (Fig 4).



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  		Figure 3. Cerebrospinal fluid flow artifact in a 60-year-old woman with lung carcinoma. Transverse FLAIR image (10,000/147/2,200) demonstrates prepontine increased signal intensity (arrows), representing pulsation artifact, which could obscure depiction of abnormal cranial nerves.

 


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  		Figure 4a. Transverse MR images in a 51-year-old man with lymphoma. (a) Gadolinium-enhanced T1-weighted MR image (600/8) reveals abnormal enhancement of the infundibular stalk (arrows). (b) FLAIR image (10,000/147/2,200) appears unremarkable.

 


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  		Figure 4b. Transverse MR images in a 51-year-old man with lymphoma. (a) Gadolinium-enhanced T1-weighted MR image (600/8) reveals abnormal enhancement of the infundibular stalk (arrows). (b) FLAIR image (10,000/147/2,200) appears unremarkable.

 
FLAIR imaging after administration of contrast material is a promising technique because of the contribution of T1 shortening to the FLAIR image (6). It generally has proved to be less useful than contrast-enhanced T1-weighted imaging in assessing parenchymal masses (6,18), particularly metastases (19). However, contrast-enhanced FLAIR images recently have been shown to be superior in the detection of sulcal or meningeal infection or inflammation (6). Further investigation is needed to see if contrast-enhanced FLAIR imaging is superior to contrast-enhanced T1-weighted imaging in depicting metastatic disease of the leptomeninges: specifically, whether the benefits of contrast-enhanced FLAIR imaging for sulcal lesions outweigh the limitations in other extratransverse locations.

In conclusion, although FLAIR images depict leptomeningeal abnormalities that are not apparent on images obtained by using other MR sequences, contrast-enhanced T1-weighted images are more sensitive in the setting of neoplastic leptomeningeal disease. FLAIR imaging has comparative limitations in depicting cisternal and cranial nerve lesions.


   FOOTNOTES
 
Abbreviation: FLAIR = fluid-attenuated inversion recovery

Author contributions: Guarantors of integrity of entire study, S.K.S., L.E.G.; study concepts, S.K.S., N.E.L.; study design, J.M.A., L.E.G.; definition of intellectual content, N.E.L.; literature research, S.K.S.; clinical studies, S.K.S., J.M.A.; data acquisition and analysis, S.K.S., L.E.G.; manuscript preparation, S.K.S.; manuscript editing and review, S.K.S., L.E.G.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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