Primary fourth ventricular B-cell lymphoma in an immunocompetent patient

Letter to the Editor.

The patient is a 60-year-old woman with a history of infiltrating ductal adenocarcinoma of the left breast underwent a left partial mastectomy and left sentinel node biopsy. She presented with the new onset of diplopia 3 months later. A magnetic resonance (MR) image of the brain demonstrated an ovoid fourth ventricular mass that was homogeneously enhancing with contrast material and extended from the left lateral recess of the fourth ventricle to the adjacent paramedian cerebellum without obstructive hydrocephalus ( Figure 1). Computed tomographic (CT) scans of the chest, abdomen and pelvis with and without contrast material were within normal limits.
The patient underwent a posterior fossa craniotomy for removal of the fourth ventricular tumor. Pathologic examination of the tumor revealed discohesive, large, pleomorphic cells that were strongly immunoreactive for CD45, CD20 and CD10 proteins, with a Ki-67 proliferation index of nearly 100% ( Figure 2). Tumor cells were weakly immunoreactive for B-cell lymphoma 2 (bcl-2), B-cell lymphoma 6 (bcl-6), and paired box protein (PAX-5), had rare reactivity for multiple myeloma oncogene 1 (MUM-1) (less than 30% tumor cells), and were negative for CD34, lysozyme, CD3, myeloperoxidase, glial fibrillary acidic protein, synaptophysin, S-100 and EMA. This tumor lacked the angiocentric distribution of lymphoma cells that is classically described for intraparenchymal PCNSLs [9]. There was demarcation of the main tumor mass from the adjacent brain tissue, which had a few scattered lymphoma cells present. In situ hybridization studies showed bcl-6 gene translocation, in the absence of bcl-2 and C-MYC gene translocations. A quantitative real-time polymerase chain reaction (PCR) study showed clonal immunoglobulin heavy locus (IgH) gene rearrangements. These findings confirmed the diagnosis of a diffuse large B-cell lymphoma (DLBCL) type of PCNSL. This patient had a serum complete blood count within normal limits and multiple bone marrow biopsies and cerebral spinal fluid specimens that were negative for lymphoma. Additional body CT scan, positron emission tomographic scan and bone scan did not show any evidence of adenopathy or metastatic breast cancer. She was placed on the DeAngelis chemotherapy protocol [10] and tolerated the protocol well. Six months postoperatively, she is clinically well with no sign of recurrence.
Three cases of solitary PCNSL arising in the fourth ventricle have been previously reported [5,6,7]. The first case was a 17-year-old woman with a clinical presentation of meningitis, and the tumor was diagnosed post-mortem [7]. The second case was a 33-year-old woman with headaches and vertigo [5]. MR imaging revealed a homogeneous fourth ventricular B-cell lymphoma that was completely excised. The third case was a 69-year-old man with a clinical presentation of 6 weeks of intractable vomiting [6]. MR imaging showed a homogeneously enhancing mass in the caudal fourth ventricle. Surgical excision was performed, and pathological examination demonstrated a high-grade B-cell lymphoma.
Our case, along with the other reported cases [5,6,7], showed that PCNSL can arise in rare instances from the fourth ventricle as a solitary mass lesion ( Table 1). All four patients were immunologically competent, with ages ranging from 17 to 69 years. Clinical presentation involves symptoms secondary to cerebellar mass effect, including headaches, vertigo, vomiting and diplopia. These tumors are homogeneously enhancing on  The origin of these solitary fourth ventricular PCNSLs remains uncertain. In our case, the main tumor mass was demarcated from adjacent brain tissue. There were only a few scattered lymphoma cells present in the adjacent brain tissue. The typical angiocentric infiltration pattern of the PCNSL [9] was not present in this tumor. The immunohistochemical studies showed that the tumor has a germinal center B-cell-like profile (bcl-2+/ bcl-6+/CD10+), which is consistent with the typical PCNSL. However, the MUM-1 immunoreactivity was only focal and patchy (less than 30% of the tumor cells). This is different from the typical PCNSL, which has near 100% MUM-1 strong immunoreactivity [11].
In rare instances, PCNSL can occur as a solitary mass lesion in the fourth ventricle.
Primary B-cell lymphoma should be included in the differential diagnosis of posterior fossa mass lesions, including lesions identified in immunocompetent patients. Given the immunohistologic differences between our specimen and the classic description of PCNSL tissue, additional studies are needed to further characterize these solitary fourth ventricular PCNSLs when more cases become available.