Characteristics of Intravascular Large B-Cell Lymphoma on Cerebral MR Imaging

Infarctlike Lesions

Infarctlike lesions suggest that the tumor predominantly involves small arteries.¹¹ This pattern was reported in 36% of the patients with IVL who had brain MR imaging.⁷ Although infarctlike lesions were observed in only 2 patients in our study (2/11), 4 of the 5 postmortem examinations, including those of 2 patients without infarctlike lesions on MR imaging, revealed multiple infarctions and severe vascular occlusions by tumor cells. The low frequency of infarctlike lesions may be explained by the timing of pretreatment MR imaging and the stage of the disease.

Nonspecific White Matter Lesions

Poorly defined nonspecific white matter lesions have been reported, especially in the periventricular area, and our study showed a similar distribution.^7,12 In the 2 patients with this pattern, the signal intensity decreased in 1 patient after treatment started and increased in the other patient who went without treatment for IVL. Postmortem examination revealed leukoencephalopathy and severe tumor cell infiltration. The small vessels severely occluded by tumor cells observed at postmortem examination were much more frequent than the number of infarct foci on MR imaging. Usually the tumor cells are noncohesive and free in the lumina in IVL, but the pathogenesis of this pattern has been described as sluggish flow within the lumens of capillaries or microinfarcts.¹² We speculate this pattern is caused by congestion and chronic ischemic change due to severe vascular infiltration by tumor cells.

Meningeal Enhancement

Meningeal enhancement is sometimes present in patients with IVL, though the nature of the finding has not been determined.⁷ Thrombus formation, vasculitis with lymphocyte infiltration, and fibrous thickening of the outer layer of small vessels have been reported in the cerebral vessels at postmortem examination.^2,13 Postmortem examination of cases in this study showed a severe meningeal inflammatory reaction with tumor cells. This pathologic finding suggests the invasion pathway of lymphoma cells to the extravascular structure.

Masslike Lesions

Intraparenchymal masslike lesions presented with extensive vasogenic edema and mass effect, contrary to the characteristic features of tumor cell infiltration predominantly in the vascular lumen. The response to therapy strongly suggested that the lesions were caused by IVL. Masslike lesions have been described in previous reports as representing extravascular spread of lymphoma cells with accompanying inflammatory change in vascular walls and surrounding parenchyma with microinfarct.^2,3,7,14,15 Extravasation of lymphoma cells and vascular wall thickening with direct infiltration of tumor cells into the vascular walls were present at postmortem examination. The pathologic change behind this pattern may be multifactorial.

Hyperintense Lesions in the Pons on T2WI

Hyperintense lesions in the central pons on T2WI without enhancement or diffusion restriction were observed in 5 of 11 patients with IVL before treatment. This pattern in patients with IVL has not previously been reported in English-language literature, to our knowledge. The decrease of the lesions seen on MR imaging in 4 patients after treatment started strongly suggests that these lesions are a manifestation of IVL. The hyperintense lesions in the central pons, excluding the pontine tegmentum and ventrolateral region, on T2WI are similar to findings in pontine osmolytic demyelination syndrome and PRES in the brain stem or intracranial dural arteriovenous fistula with venous congestion.^16–20 Five patients showing hyperintense lesions in the central pons on T2WI had no indication of osmolytic demyelination syndrome or typical PRES. Although there was no correlating pathologic evidence from the patients who presented with this pattern, 2 of the 5 postmortem examinations on other patients showed tumor cell infiltration into the vessels including the pons (Fig 6). We speculate that vascular occlusion in small veins and arteries by tumor cells results in venous congestion that could manifest as hyperintensity in the central pons on T2WI.

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Fig 6.

Case 3. Tumor cell infiltration into the pontine vessels in an 84-year-old man. Pathologic specimen shows lymphoma cell infiltration into the capillaries in the pons (black arrows) (hematoxylin-eosin, original magnification ×50).

Cerebral MR imaging findings in patients with IVL may be diverse, but when considered in conjunction with pathologic findings, the various MR imaging findings can be logically interpreted. When occlusions occur in small arteries, one can expect multiple small infarctions such as the infarctlike lesions seen on MR imaging in this study. Occlusion in capillaries would cause diffuse white matter abnormal intensities. We speculated that the hyperintense lesions in the pons were also a result of occlusion of capillaries in the pons as was observed at postmortem examination in case 3. When large numbers of lymphoma cells cause extravascular mass, masslike lesions can be expected. Thickening of the meningeal vessels with some inflammatory reaction would present as meningeal enhancement. Attention to the intravascular nature of this unique lymphoma could lead to better recognition of the various MR imaging appearances and a more timely diagnosis.

This study has several limitations. The number of patients is small due to the rarity of this tumor, and radiologic follow-up is short. Cerebral postmortem examination was performed in 5 cases, including 1 case in which only the bilateral frontal lobes were examined. Brain tissue was not taken from the remaining 6 cases. Masslike lesions and hyperintense lesions in the pons on T2WI were not pathologically proved in this study. Brain biopsy is often difficult in patients with severe conditions, and postmortem examination might be the only way to analyze these patterns.