Figures 1 and 2: There is a large mass measuring 4 x 2 cm involving the bifrontal white matter and corpus collosum. This mass has a heterogeneous appearance with a central area of high T2 signal intensity surrounded by a band like area of hypointensity. There is mass effect upon the adjacent sulci.

Figures 3A, 3B, and 4: Post-contrast T1-weighted imaging demonstrates that the previously mentioned central area of high-T2 signal has low signal intensity suggestive of central necrosis or cystic components. The band like area of hypointensity on T2-weigthed imaging demonstrates bright enhancement on post-contrast T1-weighted images.

Figure 5: Patient is post-treatment with steroids and chemotherapy. Axial FLAIR image demonstrates some residual signal abnormality. There is focal volume loss in the affected area but there is decreased mass effect upon the adjacent sulci.

Figures 6 and 7: Patient is post treatment with steroids and chemotherapy. Post-contrast images demonstrate no residual contrast enhancement of the mass.

Primary CNS lymphoma (Non-Hodgkin’s B-cell lymphoma).

Lymphoma involving the central nervous system (CNS) can be primary or may occur as metastasis from systemic lymphoma. Primary central nervous system lymphoma (PCNSL) is more common and refers to the isolated involvement of the craniospinal axis in the absence of primary tumor elsewhere in the body. Histologically, primary CNS lymphomas are almost exclusively intermediate to high-grade non-Hodgkin’s lymphoma of B cell origin. Primary CNS lymphoma accounts for .2 to 2% of all primary CNS malignancies, however its incidence is increasing dramatically due to an increase in sporadic occurrence and within the patient population with acquired immunodeficiency syndrome (AIDS). The incidence in immunocompetent patients is approximately 51 per 10,000,00 per year, with a male predominance (male to female ratio of 2:1) and the median age of presentation at 55 years of age. The incidence of PCNSL in patients with HIV ranges from 6-20%. Almost 95% of HIV infected patients with PCNSL are males and the median age at presentation is 35 years. Other risk factors for the development of primary CNS lymphoma include transplant patients on immunosuppressive drugs and patients with congenital immunodeficiency syndromes, such as Wiskott–Aldrich syndrome, severe combined immunodeficiency (SCID), and X-linked immunodeficiency. The Epstein-Barr virus is thought to play a role in the development of PCNSL in immumocompromised patients, however the etiology in immunocompetent patients remains unknown.

The presenting symptoms in primary CNS lymphoma vary depending on location of the tumor mass and the immune status of the patient. In immunocompetent patients, the most typical presentation is progressive focal symptoms indicative of a mass lesion. Other symptoms include seizures, raised intracranial pressure, and nonspecific mental status changes. Behavioral and personality changes and confusion are common in elderly patients. Patients with HIV often present with an acute change in mental status and an encephalopathy-like picture.

At the time of patient presentation, primary CNS lymphoma can present in a variety of ways including solitary or multiple discrete intracranial nodules, diffuse meningeal or paraventricular involvement, uveal or vitreous involvement, and localized intraspinal masses. In immunocompetent patients primary CNS lymphoma most often presents as a large solitary hemispheric mass. Predominant locations of lymphoma deposits include the deeper parts of the frontal and parietal lobes, basal ganglia, corpus callosum, paraventricular region, and thalamus. The cerebellum and brainstem can also be involved. These tumors have a propensity to be found in close proximity to the corpus callosum and have a tendency to extend across the corpus callosum into the opposite hemisphere, a feature that mimics glioblastoma multiforme. The disease tends to spread along the perivascular spaces, with parenchymal lesions seen as ill-defined masses with irregular borders. Tumor extension to the ependymal and subarachnoid surfaces is also common. The tumors are often solid and usually stimulate less vasogenic edema than metastatic tumors or high grade gliomas. Hemorrhage, calcification, necrosis, and cyst formation are also uncommon. The differential diagnosis of a patient with suspected PCNSL depends on the patient’s immune status and the radiologic appearance of the lesion. In immunocompetent patients the differential of a solitary mass may include high-grade primary brain tumor (e.g. glioblastoma multiforme), isolated metastasis, and multiple sclerosis. In an AIDS patient the differential may include opportunistic infections such as toxoplasmosis or cytomegalovirus. Immunocompromised patients can also have lesions of multiple etiologies simultaneously e.g. infection and neoplasia.

The imaging characteristics of primary CNS lymphoma can also vary with the patient’s immune status. In immunocompetent patients, MR imaging demonstrates intermediate to low signal intensity tumor on T1-weighted images. On T2-weighted images, these tumors can have either an isointense or hypointense signal relative to gray matter. These lesions can also demonstrate mass effect and mild or moderate amount of peritumoral edema. On post-contrast images, intense homogeneous enhancement of a solitary mass is the hallmark of primary CNS lymphoma in the immunocompetent patients. Post-contrast images can also demonstrate leptomeningeal disease. Detection of enhancement along perivascular spaces on MRI should put PCNSL on top of the differential diagnosis. Hemorrhage, calcification, necrosis, and cyst formation are uncommon imaging findings for primary CNS lymphoma. Greater than half of patients with HIV present with a supratentorial parenchymal mass with frequent involvement of the corpus callosum, basal ganglia, and other deep cerebral nuclei. Primary CNS lymphoma in these patients more commonly appears as multifocal lesions with ring enhancement and with more prominent edema than in immunocompetent patients. Contrast enhancement is variable and is commonly in an inhomogeneous pattern. Tumors with necrotic centers are more often seen in the AIDS population. In addition, primary CNS lymphomas in HIV patients may appear cavitary and thus be indistinguishable from other abnormalities such as opportunistic infections

Cerebral lymphomas are very radiosensitive and respond dramatically to steroid therapy. They usually show an excellent initial response to radiation and chemotherapy, which combined are the primary treatments used for primary CNS lymphoma. The tumor may “melt away” giving rise to the nickname “ghost tumors.” It is important to note that steroid treatment can result in marked shrinkage of these lesions, with loss of contrast enhancement in a relatively short period of time. Recurrence is very common and most patients die from this disease. Survival time following treatment varies from 1-3 years.

References:

1. Atlas, Scott W. Magnetic Resonance Imaging of the Brain and Spine, 3rd Ed. Philadelphia: Lippincott Williams & Wilkins, c2002. pp. 404-407, 446-448.
2. Pruitt, AA. Primary CNS Lymphoma. eMedicine, 2003.
3. Erdag N, Bhorade RM, et al. Primary Lymphoma of the Central Nervous System: Typical and Atypical CT and MR Imaging Appearances. American Journal of Roentgenology. 2001; 176: 1319-1326.
4. Buhring U, Herrlinger U, et al. MRI Features of Primary Central Nervous System Lymphomas at Presentation. Neurology. 2001; 57: 393-396.
5. Behin A, Hoang-Xuan K, et al. Primary Brain Tumours in Adults. Lancet. 2003; 361: 323-31.
6. Sator K. MR Imaging of the Brain: Tumors. European Radiology. 1999; 9: 1047-1054.