Discussion
WM is a rare hematologic malignancy accounting for 1-2% of monoclonal gammopathy and
associated to lymphoplasmacytic lymphoma in the WHO classification [9, 10]. This B cell lymphoproliferative disorder is defined by the infiltration of lymphoplasmacytic cells into bone marrow and the demonstration of immunoglobulin M monoclonal gammopathy [4, 8]. Neurologic symptoms occurring in 25% of cases are commonly related to serum hyperviscosity or autoimmunologic phenomena [8]. However, a malignant infiltration of the CNS by lymphoplasmacytic cells remains extremely rare and defines Bing-Neel syndrome. Two Danish physicians namely Jens Bing and Axel Valdemar Neel first demonstrated this exceptional condition in 1936 [7, 8]. According to a literature review, there was only 33 cases of BNS until 2010 on Pubmed. Simon et al reported 44 cases of BNS in a multicenter study and gave a literature review of 33 cases from 1995 to 2014 [11]. However, this last decade (2015 to 2024) showed a great interest for BNS With 105 cases found on Pubmed research out of 154 reported. so far. BNS consists in either diffuse or tumoral form as in our case [1, 2, 4, 7, 8]. Tumoral BNS is often consistent either with intraparenchymal process suggestive for glioma, or meningeal infiltration [8, 9]. Thus, extra axial appearance is very rare and, to the best of our knowledge, only 3 cases of BNS mimicking meningioma are reported in the literature and our case displays the biggest size [6]. The clinical presentation of the tumoral BNS is similar to other space occupying lesions and usually consists of focal deficit or seizure [1, 2, 8, 9, 10]. Diffuse BNS often presents with headache, memory loss, confusion, dementia or coma [1, 4, 8, 10]. In our case, the patient was paucisymptomatic despite the large size of the tumor and let foretell a long duration of evolution. BNS can occurred at any time during the course of the disease [12]. In a study of 34 cases of BNS, Castillo et al noticed this occurrence in half of WM cases within 5 years and in 18% over 10 years [12]. Fintelmann et al classified BNS into 2 categories: group A describes patients with neurologic symptoms probably as a result of lymphoplasmacytoid cells within the central nervous system (parenchyma, meninges, CSF and dura); Group B refers to BNS cases with neurological symptoms without cells (< 5 cells/mm3) within the CSF [13, 14]. Our patient may be classified as group A and some authors suggested a more important damage of blood-brain-barrier allowing the transfer of these cells from the blood to the central nervous system in this group [13, 14]. The diagnosis of tumoral BNS is based on the pathological examination of the tumor and the bone marrow biopsy associated to protein electrophoresis [1, 2, 6]. This pathological examination often demonstrates atypical lymphoid cells consisting of small lymphocytes, lymphoplasmacytic cells and plasma cells [1, 2]. Immunohistochemically, these BNS cells are B cells usually positive to CD20, CD138 and negative to CD5, CD10, CD23 [2, 7, 10]. These cells express immunoglobulin M and serum proteins electrophoresis always shows an Ig M monoclonal gammopathy [1, 2, 8]. All those pathological and proteins immunoelectrophoresis features were found in our patient. The authenticity of our presentation is highlighted by the radiological presentation. Indeed, all but three of the Bing-Neel tumors were intra-axial lesions [6, 8]. The first extra-axial tumoral BNS mimicking meningioma was reported by Civit et al in 1997 [3], the second and third was reported in 2020 and 2023. Our observation is the fourth and We failed to find a most voluminous than this latter in literature review. Because of their intra-axial location and their relatively small size, some Bing-Neel tumor requires only stereotaxic biopsy for histological confirmation [9]. In our case, the radiological diagnosis of the lesion was consistent with a giant meningioma, thus the surgical approach was justified. The treatment of tumoral BNS is based on chemotherapy, which might be associated to a focal radiation therapy [1, 2, 6]. WM shows an estimated median survival of 7-12 years, albeit BNS prognosis was still severe with a free survival rate of 12 months (0-84 months) despite a heavy therapeutic armamentarium [14, 6]. However, the outcome of tumoral BNS seems to be better than diffuse BNS [6] and more recent study revealed a survival of 5 years and 10 years of 71% and 59% [11, 14]. Castillo et al identified in univariate analysis, age above 65 years, previous treatment for WM and platelet count < 100 x 109/L as adverse prognostic factors [12]. None of these latter were found in our patient and he was asymptomatic a eighteenth month follow up.