PCNSL is a rare disease that represents approximately 6% of all malignant brain tumors and 1–2% of all lymphomas . The age of diagnosis is usually between the fifth and sixth decade of life. It is less frequent in pediatric patients, with a better prognosis in this age group than in the older population .
Acquired or congenital immunodeficiency is the best-established risk factor, and the disease usually presents as a single tumor, located mainly in the frontal lobes (20–43%) and the basal nuclei (9–13%) .
The clinical picture is variable and usually presents with a rapidly progressing neurological deficit, which varies according to the location of the tumor and occasionally leads to progressive encephalopathy . In the present case, since the patient had bilateral involvement of the basal nuclei, the main repercussions were on motor patterns.
Bilateral involvement of the basal nuclei is more common in immunodeficient patients, increasing the possibility of differential diagnosis. Lesions with this pattern of involvement may have a systemic or local cause, involving metabolic conditions, such as Wilson’s disease; neurodegenerative conditions, such as Fahr’s disease and vascular abnormalities; infectious diseases, such as toxoplasmosis; inflammatory conditions, such as Behçet’s disease; and neoplasms, such as primary lymphomas, gliomas, and various metastases .
Despite a characteristic imaging pattern in traditional MRI sequences, this method cannot differentiate PCNSL from other neoplasms or non-neoplastic diseases that affect the central nervous system. Therefore, more modern imaging modalities have been used, such as spectroscopy and positron-emission tomography (PET), which help differentiate PCNSL from other diseases in a less invasive way through their profiles of metabolic activity and biochemistry. For example, spectroscopy evidences high lipid peaks combined with high choline/creatinine ratios. PET with fluorodeoxyglucose (FDG) shows hypermetabolic lesions with increased FDG uptake . In the present case, MRI showed a homogeneous bilateral lesion evidenced by paramagnetic contrast in the basal nuclei, and spectroscopy showed choline peaks.
Lesions caused by PCNSL have higher metabolic activity than metastases and high-grade gliomas. By contrast, infectious processes usually present hypometabolic lesions in immunocompromised patients, while PCNSL has a hypermetabolic pattern with high FDG rates in PET .
In addition to imaging tests, when there is a high diagnostic suspicion of PCNSL, biopsy of the lesion with a histopathological study is the gold standard for the diagnosis of the disease and the establishment of an appropriate therapeutic plan . Because the described case featured a bilateral lesion in eloquent areas, the diagnosis was defined only after the biopsy.
In general, surgical resection of the lesions is not indicated because PCNSL is a highly infiltrative tumor. However, it is usually responsive to chemotherapy combined with radiotherapy, and early diagnosis is a predictor of the best prognosis .