Primary dural-based parafalcine diffuse large b-cell lymphoma mimicking meningioma

A 58-year-old male individual previously healthy and immunocompetent presented with headache, recurrent vomiting, and memory problems lasting for 3 days. No loss of consciousness, seizure, subjective weakness, or fever was observed. On physical examination, the patient’s Glasgow coma scale score was 15; his pupils were 3 mm in diameter, equal, and reactive; and the patient had nominal aphasia without motor and sensory deficit. He had normal cerebellar functions, and cranial nerve exams revealed no deficit. Head computed tomography (CT) (Fig. 1) showed a 2.2 × 3.8 cm (transverse × anteroposterior) iso-dense lesion with internal hypodensity in the left parasagittal frontal region extending to the right frontal region. Extensive perilesional edema was observed with effacement of the sulci and mass effect on bilateral frontal horns, associated with 3-mm midline shift. Head magnetic resonance imaging (MRI) showed an isointense parasagittal lesion on T1 and heterogeneous intense on T2, with redemonstration of perifocal edema (Fig. 2). Head T1-weighted imaging with contrast enhancement (Fig. 3) showed a large, left frontal, parafalcine, irregular-shaped mass located below the superior sagittal sinus level. It measured 4 × 3 × 3.3 cm in anteroposterior, mediolateral, and craniocaudal, respectively. It showed diffusion restriction (Fig. 4). There was central hyperintensity on T2-weighted imaging, without post-contrast enhancement area representing cyst formation. It exerts a mass effect characterized by effacement of the adjacent sulci, compression of the left lateral ventricle, and a 3-mm shift of the midline structures to the right side, and the impression of our neuroradiologist was atypical meningioma. Regarding extensive edema, dexamethasone was started at a dose of 4 mg, thrice a day, and the patient was planned for craniotomy and resection of the tumor. Initially, the patient was reluctant to undergo surgery; however, subsequently, the patient agreed to undergo surgery after approximately 10 days. During surgery, parasagittal craniotomy was performed; however, to our surprise, no definite mass lesion was found at the proposed site, in contrast to the findings described on imaging. The falx was thinned out and partly deficient. A biopsy sample was obtained from this abnormally appearing falx. Moreover, we obtained biopsy samples under neuronavigation guidance from abnormally appearing tissue, which was completely intra-axial, deep down in the lesion visualized on navigation. On postoperative day 1, MRI head with contrast enhancement (Fig. 5) showed that the previously seen lesion had a significant regression in size. Its right frontal extension and adjacent enhanced meningeal tail showed size reduction. Moreover, some regression in the perilesional vasogenic edema was observed. A significant regression in the previously described enhancement was noted at the left-side lentiform nucleus and external capsule. The MR spectroscopy study showed an increased choline/N-acetyl aspartate ratio and elevated lactate level within the lesion.

The histopathology results of the first brain biopsy samples (Figs.6–7) obtained from the falx cerebri showed meningothelial hyperplasia with calcification and focal perivascular lymphocytic infiltrate composed of small and large, atypical lymphocytes. Immunohistochemical staining was performed; however, the area of interest disappeared. The pathology team recommended another fresh biopsy to have the final diagnosis and flowmetry studies. So, the patient underwent redo craniotomy using the same incision, and multiple biopsy samples were taken. The second fresh brain biopsy (Figs. 8–9) showed multiple brain fragments with predominant perivascular atypical lymphoid infiltrates. Most cells were medium to large with moderate cytoplasm, atypical irregular nuclei having vesicular chromatin, variably prominent nucleoli, and several mitoses, including atypical one. Necrotic areas were also seen. Immunohistochemistry of the second biopsy (Fig.10 A-D) showed that atypical perivascular cells were positive for CD45, CD20, CD79a, BCl2, BCl6, MUM1, OCT2, and C-MYC, and negative for CD10, CD21, TDT, ALK1, EBV-LMP1, CD3, and CD5; however, few reactive/residual lymphocytes were positive for these enzymes. Moreover, 80% of lymphoid cellular nuclei were positive for Ki67. These findings were consistent with diffuse large B-cell lymphoma, not otherwise specified.

Whole-body positron emission tomography (PET) showed intense fluorodeoxyglucose (FDG) uptake higher than that in the healthy brain cortex, without evidence of coexisting systemic disease. In addition to PET scan, contrast-enhanced chest, abdomen, pelvis CT did not show any other lesions in the body; furthermore, workup for viral markers and autoimmune conditions were all unremarkable, thus confirming the diagnosis of “primary dural-based diffuse large B-cell lymphoma,” distinguishing it from secondary CNSL. The patient was transferred to the Oncology Department and started on three cycles of the methotrexate, cytarabine, thiotepa, and rituximab (MATRIX) protocol, which is the current standard treatment regimen for PCNSLs [5]. Three months after the diagnosis and after receiving two cycles of the MATRIX protocol, brain MRI with contrast enhancement (Fig. 11A, B) showed regression of the lesion, and PET scan showed complete metabolic resolution in terms of decreased FDG activity of the previously seen PCNSL without signs of lymphoma activity elsewhere. Subsequently, the patient received the third cycle of the MATRIX protocol without specific complications. Two weeks later, autologous stem cell transplantation (50 × 106/kg) was performed as part of the consolidation phase of treatment. Six weeks later, conditioning chemotherapy with carmustine–thiotepa was administered, followed by stem cell infusion (CD34 = 12 million/kg). The post-transplant course was complicated with mucositis, folliculitis, diarrhea, febrile neutropenia, and prolonged thrombocytopenia. Two months after transplantation, PET scan was repeated and showed complete metabolic resolution of initially seen PCNSL involvement. Currently, the patient is being followed by the hematology team; the patient is in good health and remission. The last outpatient follow-up was 8 months after the first surgery. The patient was seen by the vascular surgery (for permcath removal) and oncology teams. At this time, the patient was stable with complete remission; then, the patient was lost to follow-up. Another head MRI was performed and showed almost total regression of the lesion (Fig. 12A, B).