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Distribution of Deep Gray Matter Lesions on Magnetic Resonance Imaging in Lymphomatosis Cerebri

We herein report the distribution of gray matter lesions on magnetic resonance imaging (MRI) in two patients with lymphomatosis cerebri (LC). In our patients, the fluid-attenuated inversion recovery sequence of brain MRI demonstrated a bilateral and diffuse high signal intensity, not only in the white matter but also in the thalamus, globus pallidus, putamen, and hippocampus. Among the deep gray matter, the caudate head and putamen (striatum) were relatively spared when compared with the globus pallidus, thalamus, and hippocampus. Interestingly, we found seven previous reports of similar MRI findings, with relative sparing of the striatum, in patients with LC. This finding may be characteristic of LC and help facilitate its diagnosis. Further investigations of a larger number of LC patients are necessary to confirm these findings.


Introduction
Lymphomatosis cerebri (LC) is a rare form of primary central nervous system lymphoma (PCNSL) that predominantly involves the white matter. Pathological examinations of LC patients demonstrate the diffuse infiltration of lymphoma cells into the nerve fibers (1). Immunohistochemical studies have revealed diffuse large B-cell lymphoma in most LC patients (2). However, why LC patients present with diffuse infiltration without mass formation remains unclear.
However, the distribution of deep gray matter lesions on MRI characteristic of LC has not been reported. We herein report the distribution of deep gray matter lesions on the FLAIR sequence of MRI in two patients with LC and review the literature.

Case 1
A 67-year-old woman gradually presented with bradykinesia, followed by appetite loss and difficulty walking, and was admitted to our hospital about 1 month after the onset. She had no medical history of note. A neurological examination demonstrated a mask-like face, dysarthria, dysphagia, bradykinesia, muscle rigidity, frontal lobe sign, and pyramidal sign as well as a wide-based and short-stepped gate.
On MRI, bilateral brain lesions were most clearly demonstrated with a FLAIR sequence, which showed a high signal intensity in the brainstem, cerebellum, hippocampus, thalamus, putamen, globus pallidus, and cerebral white matter (Fig. 1). Among the deep gray matter, the caudate head and putamen (striatum) were relatively spared when compared with the globus pallidus, thalamus, and hippocampus. There was no apparent mass effect. On DWI, the lesions showed a faint high signal intensity. In an ADC map, most lesions exhibited a slight increase of the ADC values. A gadolinium-enhanced T1-weighted image (Gd-T1WI) showed abnormal enhancement from the right hippocampus to the globus pallidus ( Fig. 1).
A stereotactic brain biopsy of the right globus pallidus demonstrated the diffuse infiltration of large abnormal cells, which were immunopositive for CD20 and CD79a. A diagnosis of LC due to diffuse large B-cell lymphoma was established based on the MRI and biopsy findings.

Case 2
A 71-year-old man presented with progressive gait disorder and was admitted to our hospital about 5 months after the onset. His medical history included hypertension and chronic kidney disease. A neurological examination demon- strated time-related disorientation, miscalculation, frontal lobe sign, and upper limb apraxia as well as limb and truncal ataxia.
On MRI, bilateral brain lesions were most clearly demonstrated with a FLAIR sequence, which showed a high signal intensity in the brainstem, cerebellum, hippocampus, thalamus, caudate head, putamen, globus pallidus, and cerebral white matter (Fig. 2). Among the deep gray matter, the caudate head and putamen (striatum) were relatively spared when compared with the globus pallidus, thalamus, and hippocampus. There was no apparent mass effect. Gd-T1WI showed abnormal enhancement around the inferior horn of the left lateral ventricle and in the corpus callosum (Fig. 2).
Blood tests showed that the sIL-2R level was slightly elevated to 723 U/mL. A lumbar puncture yielded watery clear CSF. The cell count was 9/μL, comprising mononuclear cells of 8/μL and polymorphonuclear cells of 1/μL. The total protein and glucose levels of the CSF were 51 and 61 mg/ dL, respectively. The sIL-2R level of the CSF was elevated to 676 U/mL. Cytology of the CSF was negative.
A stereotactic brain biopsy from the genu of the corpus callosum demonstrated the diffuse infiltration of large abnormal cells with an angiocentric pattern, which were immunopositive for CD10, CD20, and CD79a. A diagnosis of LC due to diffuse large B-cell lymphoma was established based on the MRI and biopsy findings.

Discussion
On MRI of our patients, the FLAIR sequence clearly Intern Med 60: 623-627, 2021 DOI: 10.2169/internalmedicine.5200-20   (2), and this finding is uncommon in other diseases considered in the differential diagnosis (2). In our patients, the caudate head and putamen (striatum) were relatively spared on MRI compared with the globus pallidus, thalamus, and hippocampus. Interestingly, we found seven previous reports of similar MRI findings with relative sparing of the striatum despite involvement of other deep gray matter in patients with LC (2, 3, 5-9). This finding may be due to the fact that the nerve fibers are sparse in the striatum when compared with other deep gray matter. Fig. 3 shows the Klüver-Barrera staining (myelin staining) of a coronal section of the human postmortem brain hemisphere at the plane of the internal segment of the globus pallidus (an autopsy of this another patient was done at our hospital). This figure shows that the striatum is hardly stained compared with other deep gray matter tissues, in-cluding the globus pallidus, thalamus, and hippocampus.
In conclusion, in addition to the finding of "bilateral hemispheric lesions on the first MRI scan (2)", "relative sparing of the striatum despite involvement of other deep gray matter on FLAIR" may be characteristic of LC and provide a clue for the diagnosis of LC, although the absence of these findings does not necessarily exclude the possibility of LC. Further investigations of a larger number of LC patients are necessary to confirm these findings.