Intraventricular mass in a 52-year-old woman

A 52-year-old woman, without previous medical history, presented to our hospital with acute onset of headache, dizziness, and fatigability. Brain magnetic resonance imaging (MRI) revealed a 17.4 mm × 15.4 mm × 23.5 mm solitary, circumscribed, well-defined enhancing mass, centered on the trigone of the left lateral ventricle. Radiological findings were suggestive of intraventricular meningioma (Figure 1). The patient underwent surgery, and a gross total resection was performed. The intraoperative macroscopic findings were typical for a meningioma—the tumor was overly fibrous, well-defined, firm, encapsulated, and attached to the ventricular walls and choroid plexus.

Histological examination revealed a tumor composed of a mixture of diffuse infiltrates of medium-sized lymphocytes with rounded and angled nuclei and relatively abundant pale cytoplasm, and plasmacytoid cells with paracentric nuclei, wheel-like chromatin, and eosinophilic cytoplasm (Figure 2A, Box 1). A lymphoplasmacytic meningioma was suspected, and immunohistochemistry (IHC) was performed to confirm the diagnosis. The medium-sized lymphocytes mainly expressed CD20 (Figure 2B) and CD79a and were negative for CD5 (Figure 2C) and CD3; therefore, they could be assigned to the B-cell lineage, suggesting B-cell non-Hodgkin-lymphoma (B-NHL) accompanied by a physiological CD3, CD5 T-cell infiltrate. The B-lymphocytes and plasma cells also showed a monotypic expression of the immunoglobulin light chain kappa (kappa/lambda ratio: >10/1, Figure 2D,E). Immunohistochemically, there was no evidence of aberrant expression of CD10, BCL6, CD23, CyclinD1, MUM1, EMA, or progesterone receptor and therefore, there was no evidence of B-CLL, mantle cell lymphoma, follicular lymphoma, or meningioma. The proliferation index (Ki-67) was low (~15%, Figure 2F), consistent with the diagnosis of indolent B-NHL.

Serum protein electrophoresis and immunofixation showed no serum immunoglobulin abnormalities. A sternal bone marrow biopsy was performed, with normal findings.

Primary intraventricular marginal zone B-cell lymphoma was diagnosed.

Extranodal marginal zone lymphoma (EMZL) is an indolent, small B-cell neoplasm that can be found in any extranodal location, but most frequently in the gastrointestinal tract (MALT lymphoma). [1] In rare cases, MALT lymphomas may develop in tissues without mucosa, including the central nervous system. Ventricular invasion of a parenchymal primary CNS lymphoma occurs in up to 10.6% of cases, but an exclusively intraventricular form is very rare. [1-3].

MALT lymphomas have the ability to mimic meningiomas on imaging, dural-based masses being the most common appearance. [2] Despite the lack of mucosa in the brain tissue, it is suggested that intraventricular MALT lymphomas may be mistaken for meningiomas because arachnoid cap cells (contained within the choroid plexus) serve as a surrogate for mucosal epithelium, which is involved in MALT lymphomas. [2].

We report an exceedingly uncommon case of a primary marginal zone B-cell lymphoma (MZL) located in the atrium of the lateral ventricle, radiologically and clinically mimicking a meningioma. The well-circumscribed aspect on imaging was distinct from that of a lymphoma, a tumor that usually has an infiltrative appearance, being imprecisely delimited, with periventricular distribution, rather than purely intraventricular. Biopsy demonstrated a lymphoid infiltrate with a predominance of medium-sized B cells. The tumor showed a plasmacytic differentiation, and the main differential diagnosis was lymphoplasmacytic lymphoma, which was excluded (normal protein electrophoresis and immunofixation, no bone marrow infiltration; MYD88 mutation could not be assessed).

Complete remission was achieved after surgery, chemotherapy, and radiotherapy. To our knowledge, there are only four reported cases of intraventricular marginal zone B-cell lymphomas masquerading as meningiomas in the English literature. [2].

Due to the scarcity of cases encountered, solitary intraventricular marginal zone B-cell lymphoma may be misdiagnosed. Radiological similarities between intraventricular MZL and meningioma can lead to a delay in the appropriate therapeutic plan. In the case of a small, asymptomatic meningioma, a potential surgical intervention can be postponed, which should not be done in the case of a malignant tumor such as lymphoma, even if it is indolent. A tumor sample may be required to establish the correct diagnosis and to assess the degree of malignancy, the prognosis, and the need for oncological treatment. EMZLs display distinct pathological characteristics depending on their anatomic site; recognizing these variations is essential for accurate diagnosis and management. [1] The prognosis of primary CNS EMZL (especially nonparenchymal type) is usually favorable [1, 2]. Furthermore, the ability to perform gross total resection for primary CNS EMZL may provide a better outcome [1].

Through this case image, we aim to highlight the unusual presentation of this scarce pathology and the need to consider EMZL in the differential diagnosis of intraventricular tumors, especially when imaging suggests meningioma. Awareness of this rare entity is important so that appropriate management can be done.

Conceptualization: FMB; Data analysis and interpretation: AP, FMB, MA, LT, SO, SS, MPD; Drafting the manuscript: AP, FMB; Critical review and editing of the manuscript: SS, MPD, GEDP; Supervision: FMB, GEDP. All authors read and approved the final version of the manuscript.

Dr. Dragomir is supported by the Berlin Institute of Health Clinician-Scientist (CS Program) and by Deutschen Konsortium für Translationale Krebsforschung (DKTK) Berlin (Young Investigator Grant 2022).

The authors declare no conflict of interest.

All data related to this case are deidentified.