MRI, CT findings in ALL with leptomeningeal disease

Issue: April 10, 2011

ByMunir Ghesani, MD, FACNM

ByLauren Moomjian, MD

ByDaniel E. Meltzer, MD

A 27-year-old female with a past medical history of acute lymphoblastic leukemia presented with headache. She had previously received chemotherapy.

The initial non-contrast head CT was unremarkable. The next day, a contrast-enhanced MRI examination showed diffuse abnormal fluid attenuated inversion recovery (FLAIR) signal and enhancement throughout the sulci and basal cisterns. The non-contrast and contrast-enhanced head CT (CECT) obtained 9 days later demonstrated diffuse abnormal sulcal enhancement, with no evidence of subarachnoid hemorrhage on the non-contrast portion of the examination.

Panel A shows an axial gadolinium-enhanced T1-weighted image at the level of the midbrain; panel B shows an axial FLAIR image at the same level. There is abnormal enhancement (arrow in A) and FLAIR signal hyperintensity (arrow in B) between the folia of the superior vermis. Panel A also demonstrates abnormal enhancement along the pial surface of the brain stem (arrowhead). Panel B shows additional signal abnormality within the sulci (arrowheads).

Photos courtesy of M. Ghesani, MD

Panel A shows an axial FLAIR image at the level of the corona radiata. There is diffuse signal abnormality in the sulci (arrows), in contradistinction to the normal hypointense signal of the CSF in the ventricles. Panel B shows an axial image from the follow-up contrast-enhanced CT. Corresponding to the findings on the MRI, there is diffuse abnormal hyperdensity of the sulci (arrows).

Shown here are two axial images from the non-contrast portion of the CT examination. At the level of the internal capsules (panel A), and at the level of the pons (panel B), there is normal hypodensity of the sulci and basal cisterns (arrows in A and B), with no evidence of subarachnoid hemorrhage.

Cytologic analysis of the patient’s CSF reveals cords and sheets of leukemic cells.

Discussion

On MRI, abnormal FLAIR signal hyperintensity in the subarachnoid spaces raises three main diagnostic considerations: hemorrhage, infectious meningitis and leptomeningeal carcinomatosis. The differential diagnosis for abnormal sulcal enhancement on CECT is similar. On MRI, the post-contrast T1 enhancement of the subarachnoid spaces would not be expected for subarachnoid hemorrhage, effectively narrowing the differential diagnosis to infection vs. carcinomatosis. This is confirmed by the absence of subarachnoid hemorrhage on the non-contrast head CT.

The differential diagnosis of meningitis vs. leptomeningeal leukemic infiltration is consistent with the patient’s history of ALL, and the two disease processes are not mutually exclusive, either radiographically or clinically. Cerebrospinal fluid (CSF) microbiology showed no growth at 96 hours. From the same CSF sample, cytology was positive for ALL. The CSF cytology and microbiology results confirm the diagnosis of leukemic meningitis, in keeping with the radiographic findings and clinical history.

On MRI, leptomeningeal enhancement is characterized by high signal intensity within the subarachnoid space of the sulci and cisterns on post-contrast T1 weighted images. Although MRI with contrast is sensitive for the detection of leptomeningeal disease, the specificity is limited by the similar appearance of infectious/inflammatory and neoplastic processes; less commonly, reactive vascular engorgement or chemical irritants may produce a similar appearance. Other data, including history and physical examination, laboratory values, CSF and histopathology, must be incorporated with the MRI and CT imaging findings to make an accurate diagnosis. More than five leukocytes per microliter of CSF and CSF differential, including lymphoblasts, are diagnostic of central nervous system (CNS) leukemia.

The incidence of disease within the CNS in ALL has been reduced by the use of CNS prophylaxis. However, achievement of complete cure in ALL may be confounded by CNS recurrence. The most common form of CNS involvement in ALL is diffuse infiltration of the meninges and subarachnoid space by leukemic cells. Patients with cerebral neoplastic meningitis can present with a variety of symptoms and signs, including headache, altered mental status, nausea, vomiting, gait and sensory disturbances, cognitive deficits, papilledema, seizures and loss of consciousness.

CNS disease in ALL was historically a portent of poor outcome. More recent data from developed nations have shown a decline in relapse rates and improved outcome in cases of relapsed ALL, including relapse with CNS disease. However, this trend continues to lag in resource-poor nations.

Munir Ghesani, MD, is an attending radiologist at St. Luke’s-Roosevelt Hospital Center, and Beth Israel Medical Center and a HemOnc Today section editor. He is an associate clinical professor of radiology at Columbia University College of Physicians and Surgeons.

Daniel E. Meltzer, MD, is an assistant professor of radiology at St Luke’s-Roosevelt Hospital Center and Beth Israel Medical Center. He is an assistant professor of radiology at Albert Einstein College of Medicine.

Lauren Moomjian, MD, is a resident in radiology at St Luke’s-Roosevelt Hospital Center.

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