Demonstration of Epstein-Barr virus in primary brain lymphoma by in situ DNA hybridisation in paraffin wax embedded tissue

Epstein-Barr virus-associated primary central nervous system lymphoma in the Japanese population

The incidence of Epstein-Barr virus (EBV)-associated primary central nervous system (CNS) lymphoma in Japan was assessed using in situ hybridization of EBV-encoded small ribonucleic acid-1 (EBER-1) to identify the presence of EBV in 22 cases of formalin-fixed and paraffin-embedded primary CNS lymphoma. All cases were B-cell lymphoma. EBER-1 expression was observed in the nuclei of 3 of 22 primary CNS lymphoma cases (13.6%). The incidence of EBV-positive lymphoma in Japanese cases is higher than previously reported from Western countries. Patients with EBV-positive primary CNS lymphoma showed shorter survival than those with negative tumors (median 4 months vs. 26 months). EBER-1 in situ hybridization for the detection of EBV infection is rapid and reliable. Infrequent association suggests a different pathogenetic mechanism in the evolution of these tumors. Geographical differences in the incidence of EBV-associated primary CNS lymphoma may reflect epidemiological factors.

EBV-associated lymphoma and chronic inflammatory demyelinating polyneuropathy in an adult without overt immunodeficiency

Epstein-Barr virus (EBV)-associated lymphoproliferative disease occurs almost exclusively in immunocompromised states. This type of malignancy nevertheless developed in a woman without overt immunocompromise. She presented with rapidly progressive lower extremity weakness that was consistent with a chronic inflammatory demyelinating polyneuropathy (CIDP). CIDP has been documented in Hodgkin's disease but rarely in non-Hodgkin's disease. Diagnosis was confirmed by lymph node and sural nerve biopsies and by nerve conduction studies. Prednisone, rituximab, cyclophosphamide, doxorubicin, and etoposide were administered with regression of lymphadenopathy and improvement in neurologic symptoms. EBV-associated lymphoproliferative disease can thus develop in the absence of overt immunodeficiency and may trigger a demyelinating polyneuropathy.

Epstein-Barr virus meningoencephalitis with a lymphoma-like response in an immunocompetent host

We report the clinical and neuropathological findings in an immunocompetent 19-year-old patient with a fatal acute Epstein-Barr virus (EBV) meningoencephalitis and a lymphoma-like B-lymphocyte response. Our results suggest that an immunotoxic rather than direct viral neuronal invasion mediates brain damage in EBV encephalitis and rule out primary central nervous system lymphoma (PCNSL) in our patient. We discuss immunosuppression as a therapeutic option, because present strategies mainly consist of symptomatic therapy due to unclear pathogenesis and nonavailability of effective antiviral agents.

Primary central nervous system lymphomas in immunocompetent individuals: histology, Epstein-Barr virus genome, Ki-67 proliferation index, p53 and bcl-2 gene expression

Epstein-Barr virus (EBV) has been detected in the large majority of HIV-related primary central nervous system lymphomas (PCNSL) suggesting a pathogenetic role of the virus. Unlike HIV-related PCNSL, conflicting data exist with regard to the presence of EBV in non immunodeficiency-related (sporadic) PCNSL. For this reason, a population based material of 41 sporadic PCNSL was analysed for the presence of EBV genome (EBER, BHLF) using RNA in situ hybridisation (RISH). Furthermore, the expression of the gene products of the bcl-2 oncogene and the p53 tumor suppressor gene and the tumor growth fraction reactive with the monoclonal antibody Ki-67 have been evaluated. All cases but two were EBV genome negative. In the two positive cases less than 5% of tumor cells showed EBER positivity. In contrast, more than 75% of cells morphologically belonging to the tumor-cell population stained positively for EBER in two cases of HIV related PCNSL. Immunostaining for the bcl-2 oncoprotein was positive in 28 (72%) of 39 cases examined. In most cases more than 75% of tumor cells showed cytoplasmic expression. Of 37 cases investigated for p53 expression, 21 (57%) stained positively. However, in the large majority of positive cases less than 10% of the neoplastic cells stained. The percentage of Ki-67 positive cells ranged between 10% and 80% with a mean of 50%. The expression of the p53 and bcl-2 oncoproteins and the growth fraction did not have any prognostic impact. We conclude that the EBV genome is rarely detected in sporadic PCNSL, indicating that a pathogenetic role of EBV is unlikely. Like extracerebral B-cell lymphomas a large fraction of PCNSL expresses the p53 and bcl-2 oncoproteins, a feature, however, which does not seem to have prognostic implications.

Comparative analysis of Epstein-Barr virus (EBV) detection by nested-PCR and non-isotopic in situ hybridization in nasopharyngeal carcinoma (NPC)

The aims of this study were two-fold: first, to assess the relative diagnostic performance of non-isotopic in situ hybridization (ISH) and the nested polymerase chain reaction (nested-PCR) applied to Epstein-Barr virus (EBV) detection in a series of 55 unselected nasopharyngeal carcinoma (NPC) cases and, secondly, to correlate these data with histopathological classification. Our study shows that in 76.36% of NPC cases positive nuclear signals were observed using EBV-ISH. Overall, EBV-ISH positivity varied according to histological type, in that undifferentiated carcinomas showed a higher proportion of positive cases than differentiated cell carcinomas, although ISH results do not show significant differences in relation to histological types when employing two different schemes (WHO and Micheau). However, in adequate quality DNA samples (54 NPC cases), EBV-DNA was detected in 100% of cases using a nested-PCR, supporting the previous view that all histological types of NPC are in reality variants of EBV-infected neoplasia. ISH-negative cases probably reflect a lower sensitivity than PCR, particularly when a small number of viral copies are present, as well as a variable technical effectiveness for detected EBV, independent of the NPC histological type.

Hepatitis C virus and non-Hodgkin's lymphomas

The etiology of non-Hodgkin's lymphomas (NHL) remains a controversial matter, but, in the last few years, considerable evidence suggests that aberrations of the immune system and viruses may act as etiologic agents, in at least some cases of NHL. In fact, patients with primary immuno-deficiencies, or those suffering from diseases characterized by autoimmune dysfunction, show an increased risk for the development of NHL. Several viruses have been identified as possible etiologic agents for NHL; one of the best studied is the Epstein-Barr virus, which was detected in cultures of tumor cells from patients with Burkitt's lymphoma. The pathogenetic potential of this virus is illustrated by its association with an increasing number of malignant diseases. In addition, the human T-cell lymphotropic virus family (HTLV), was also recognized as possible etiologic agents for several lymphomas, such as cutaneous T-cell lymphoma and T-cell leukemia-lymphoma syndrome (HTLV-I), and T-cell hairy cell leukemia (HTLV-II). Recently, the presence of hepatitis C virus infection has also been recognized in several hematological malignancies such as mixed cryoglobulinemia, low-grade malignant lymphomas and Waldenström's disease. The possible etiopathogenetic role of this virus in non-Hodgkin's lymphomas is discussed on the basis of molecular, clinical, and epidemiological considerations.

Pathogenesis and classification of primary central nervous system lymphoma: an update

Primary central nervous system lymphoma has undergone a remarkable increase in incidence over the last decade, both in immunosuppressed and immunocompetent individuals. Its clinicopathologic evaluation requires knowledge of current hematopathologic systems for lymphoma classification, as well as specific understanding of unique central nervous system determinants. In immunocompromised individuals, the tumor has a constant association with Epstein-Barr virus. The form of Epstein-Barr virus in these tumors appears to be predominantly latent, however, the precise mechanism relating virus to tumor pathogenesis is still unclear. In immunocompetent patients, risk factors and oncogenic associations are completely unknown. Critical to the formation of these tumors is the trafficking of B-cells, whether pre- or post-transformation, across the blood-brain barrier. These B-cell migrations may require perturbations to the barrier that originate in or around neural parenchyma, such as localized injury or infection.

Immune regulation in Epstein-Barr virus-associated diseases

Epstein-Barr virus (EBV) is a member of the human herpesvirus family and, like many other herpesviruses, maintains a lifelong latent association with B lymphocytes and a permissive association with stratified epithelium in the oropharynx. Clinical manifestations of primary EBV infection range from acute infectious mononucleosis to an asymptomatic persistent infection. EBV is also associated with a number of malignancies in humans. This review discusses features of the biology of the virus, both in cell culture systems and in the natural host, before turning to the role of the immune system in controlling EBV infection in healthy individuals and in individuals with EBV-associated diseases. Cytotoxic T cells that recognize virally determined epitopes on infected cells make up the major effector arm and control the persistent infection. In contrast, the options for immune control of EBV-associated malignancies are more restricted. Not only is antigen expression restricted to a single nuclear antigen, EBNA1, but also these tumor cells are unable to process EBV latent antigens, presumably because of a transcriptional defect in antigen-processing genes (such as TAP1 and TAP2). The likelihood of producing a vaccine capable of controlling the acute viral infection and EBV-associated malignancies is also discussed.

In situ hybridization in neuropathology

In situ hybridization (ISH) allows the demonstration and localization of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in tissue sections, cells and chromosomes by utilizing a specific interaction with a labelled nucleotide probe of known composition. Although this technique has been employed for many years using radiolabelled probes, the recent development of nonisotopic labelling systems and the greatly increased availability of synthetic nucleic acids has allowed an enormous expansion in the potential applications of ISH. The technique is now applicable to unfixed and fixed tissues, including archival material. The use of enzyme-linked antibody techniques to detect labelled probes has greatly increased the sensitivity of non-isotopic ISH without a loss of specificity. The successful use of ISH demands careful selection of labelled probes, adequate tissue pretreatment to allow access of the probe, control of the stringency of probe binding and a sensitive reporter system, in addition to adequate controls. The accurate localization of nucleotides in the central nervous system (CNS) has many current research applications in the study of gene expression in multiple sclerosis and other inflammatory disorders, and a wide range of neurodegenerative disorders, viral infections and neoplasms. The technique is of diagnostic value in viral disorders, particularly where multiple infections occur. The combination of non-isotopic ISH with immunocytochemistry electron microscopy and quantitative image analysis greatly increases its research potential, while the development of a related method, the in situ polymerase chain reaction, offers an additional opportunity for further enhancing the sensitivity of this technique.

Primary central nervous system malignant non-Hodgkin's lymphomas from HIV-infected and non-infected patients: expression of cellular surface proteins and Epstein-Barr viral markers

The increased incidence of primary central nervous system malignant non-Hodgkin's lymphomas (PCNSL) in HIV- and non-HIV-infected patients and the demonstration of Epstein-Barr virus (EBV) in these tumours may indicate relationships between PCNSL and EBV. Consequently expression of EBV-induced antigens and cellular markers were studied in 11 HIV-infected and seven non-infected patients by in situ hybridization (ISH) and immunocytochemistry in monoclonal B cell PCNSL. In HIV-infected patients EBV genome was present in 9/11 cases, LMP in 11/11 cases and EBNA2 in 10/11 cases. The expression of adhesion and activation molecules was low or absent. In HIV non-infected patients, EBV genome was present in 5/7 cases, with LMP in 4/7 cases. EBNA2 was never detected. All these lymphomas expressed LFA1beta. Whatever the population, no lytic cycle EBV markers were detected. Compared with other types of EBV lymphomas, our results suggest a different EBV latency state in primary B cell lymphomas of the CNS from HIV-infected or non-infected patients.

Primary central nervous system lymphomas. Immunophenotypic, virologic, and cytogenetic findings of three patients without immune defects

BACKGROUND

Primary central nervous system (PCNS) lymphoma is a relatively rare disease, but an increasing incidence is reported. The Epstein-Barr virus (EBV), which is often found in lymphomas of immunocompromised patients, has been implicated in the development of lymphomas. Many cytogenetic analyses of nodal B cell lymphomas have been performed, but few studies on PCNS lymphomas have been reported.

METHODS

The detection of EBV genome using the polymerase chain reaction (PCR) method and cytogenetic studies were performed, in addition to histopathologic and immunophenotypic approaches in biopsied tissue from three patients with PCNS lymphoma. Immunosuppressive states and exposure to mutagens were not clear in all patients.

RESULTS

Histopathologic examination disclosed a diffuse type of malignant lymphoma in all patients. Immunophenotypic studies revealed B cell phenotype in all patients, two of whom showed positive reaction for CD5. The PCR method revealed no involvement of EBV genome in tumors in any patients. The cytogenetic study showed clonal chromosome abnormalities in all patients, and abnormalities of chromosome 1 (1q21), 6 (-6, 6q15 and 6q21), 7 (-7 and 7p15), and 14 (14q24 and 14q32) were prominent. The t(6;14)(q15;q32) observed in Patient 1 is the first case to be reported in human de novo lymphoma.

CONCLUSIONS

These findings indicate that the causative role of EBV in PCNS lymphoma without immune defects is not clear. The cytogenetic findings were similar to those observed in nodal B-cell lymphoma, suggesting that the origin of PCNS lymphoma cells does not differ from nodal B cell lymphoma cells cytogenetically.

Epstein-Barr and human immunodeficiency viruses in acquired immunodeficiency syndrome-related primary central nervous system lymphoma

The prevalence of Epstein-Barr virus (EBV) and human immunodeficiency virus (HIV) in acquired immunodeficiency syndrome (AIDS)-related primary central nervous system (CNS) lymphoma was examined. Deoxyribonucleic acid (DNA) extracted from 12 formalin-fixed, paraffin-embedded tumors was used as substrate for the polymerase chain reaction (PCR). Targets for amplification were the EBNA-1 region of EBV, the gag region of HIV, and a single copy cellular sequence as a control. The cases studied were autopsy and surgical specimens collected between the years 1985 and 1989. By the working formulation for non-Hodgkin's lymphomas, five had large cell, four had mixed large and small cleaved cell, two had small cleaved cell, and one had an unclassified histology. Epstein-Barr virus was detected in 6 of 12 tumors studied. Human immunodeficiency virus was not detected in any of the tumors. The presence of EBV was not correlated with any particular histologic tumor type. It is concluded that EBV, not HIV, can be detected in a large percentage (50%) of AIDS-related primary central nervous system (CNS) lymphomas. This viral association may be significant in light of the demonstrated ability of EBV to induce lymphoid tumors in experimental mammalian systems.

In situ hybridization: a valuable tool in diagnostic pathology

In situ hybridization or hybridohistochemistry has evolved in recent years in a new histologic modality. In situ hybridization (ISH) can be used for the detection of DNA (DISH) or RNA (RISH). The potential diagnostic value within a pathologic setting are well recognized. In this review paper, we summarize the use of DISH in a pathologic setting for the detection of chromosomal aberrations and localization of DNA-viruses like cytomegalovirus and Epstein Barr virus. RISH which is still in a more experimental stage can be applied for the localization of RNA-virus, like human immunodeficiency virus. However, the most important application of RISH will be the detection of gene-expression at the level of mRNA. Potentially this has many applications especially in early diagnostics of neoplastic tissues. Finally, we have summarized some pitfalls which may hamper the introduction of in situ hybridization for diagnostic purposes and some future developments in ISH.

Primary cerebral lymphoma: a study of 47 cases probed for Epstein-Barr virus genome

AIMS

To determine the prevalence of Epstein-Barr virus genome in primary cerebral lymphomas occurring in the absence of immune suppression.

METHODS

Forty eight consecutive patients with lymphomas restricted to the central nervous system were identified, all of whom had had neurosurgical biopsies performed at the National Hospitals for Neurology and Neurosurgery, London. Only five patients had some form of underlying immune deficiency; 43 were apparently normal. The tumours were studied with immunohistochemical markers and by in situ hybridisation, using a biotinylated probe to the internal repeat region of Epstein-Barr virus.

RESULTS

All the lymphomas were B cell in origin. Tumours from the five immunosuppressed patients all showed hybridisation, as did two of the "spontaneous" tumours.

CONCLUSIONS

This is the largest series of cerebral lymphomas so far probed for Epstein-Barr virus genome: as more are examined, it is suggested that a small proportion of the tumours from immunocompetent patients will also contain the virus.

A survey of Epstein-Barr virus gene expression in sporadic non-Hodgkin's lymphomas. Detection of Epstein-Barr virus in a subset of peripheral T-cell lymphomas

This study analyzes the association of Epstein-Barr virus (EBV) with non-Hodgkin's lymphoma (NHL) arising in patients without pre-existing overt immunodeficiency. The authors examined 201 lymphomas (105 high-grade B-cell, 82 peripheral T-cell, 7 high-grade non-B-cell, non-T-cell, and 7 hairy-cell leukemia) for EBV gene expression by immunohistologic procedures using monoclonal antibodies to EBV latent, immediate early, and replicative infection antigens. Transformation-associated EBV latent membrane protein 1 (LMP 1) was detected in 13 (6%) NHL, comprising 4 (4%) high-grade B-cell, 8 (10%) peripheral T-cell, and 1 non-B-cell, non-T-cell lymphomas. Anaplastic large-cell lymphoma of T-cell type was consistently LMP 1-negative. EBV nuclear antigen 2 was demonstrated in only three (1%) cases. Induction of replication as defined by expression of the immediate early BamHI Z leftward reading frame 1 (BZLF1) protein was detected in five cases, but early (EA) and late (VCA and MA) lytic cycle antigens were only found in two cases and in one case, respectively. The presence of EBV was confirmed by in situ DNA hybridization in 9 of 11 EBV antigen-positive lymphomas. This study shows the surprisingly frequent presence of EBV in peripheral T-cell NHL in European patients without pre-existing overt immunodeficiency. Interestingly, most sporadic B-cell NHL are not associated with the virus. Furthermore, the usefulness of selected monoclonal antibodies for the routine immunohistological diagnosis of EBV infection was confirmed.

Demonstration of Epstein-Barr virus genome in neoplastic cells of Hodgkin's disease by in situ hybridization, in paraffin-embedded tissue using biotinylated probes. A study of 46 cases

Paraffin-embedded tissue specimens from 46 cases of Hodgkin's disease (HD) were studied by in situ hybridization with biotinylated probes for the presence of EBV genomes. EBV specific DNA sequences were detected in the nuclei of Reed-Sternberg (RS) and Hodgkin cells (H), in 14 of these 46 cases. There was no correlation between positive hybridization and morphological subtype or site of tumor. By demonstrating an exclusive localization of the viral DNA in the tumor cells of HD, our study adds to the growing body of evidence to suggest an involvement of EBV in the pathogenesis of at least some cases of HD.

Primary central nervous system lymphoma

Primary central nervous system lymphomas (PCNSL) are uncommon neoplasms accounting for less than 2% of brain tumours. Their incidence appears to be increasing across a wide age range, in both immunocompetent and immunosuppressed populations. Particular risk groups include those with congenital and acquired immunodeficiencies and transplant recipients. The spread of the AIDS epidemic has seen large numbers of complicating PCNSL develop. Epstein-Barr virus infection appears to play a role in the development of these lymphomas in the immunosuppressed population. The aetiology of these tumours in the immunocompetent is uncertain. Their tendency to remain within the nervous system is not well understood but may be a function of CNS binding molecules carried by lymphocytes. Clinically PCNSL may present with a wide variety of signs and symptoms and has a capacity to mimic many other neurological conditions. Radiologically they appear as hyperdense homogenous deposits in subcortical white matter. Although most lesions are intermediate or high grade B cell lymphomas, T cell lymphomas are being recognised with increasing frequency. Immunohistochemistry and genotypic analysis have an important role in accurately characterising PCNSL, particularly in stereotactic biopsies. Involvement of multiple areas of the neuraxis, the eye and multiple intracranial sites can occur in the absence of obvious systemic lymphoma. The role of surgery in their treatment is uncertain. A combination of radiotherapy and chemotherapy can increase the length of survival. The prognosis, however, remains poor in comparison with nodal lymphomas, and particularly so in those with AIDS.

Analysis of African Burkitt's and high-grade B cell non-Burkitt's lymphoma for Epstein-Barr virus genomes using in situ hybridization

We investigated the association of Epstein-Barr virus (EBV) with African cases of Burkitt's lymphoma (BL) and high grade B cell non-Burkitt's lymphoma (non-BL) occurring in areas where BL is endemic. The presence of EBV genomes was analysed in 24 cases using in situ hybridization with a 35S-labelled EBV probe applied to paraffin sections. EBV DNA was detected in each of 10 cases of BL in which technically satisfactory results were obtained, the virus being homogeneously distributed in all identifiable tumour cells. Two other cases of BL could not be evaluated because of technical problems. In contrast, EBV DNA was not detected in any case of high-grade non-BL (10 centroblastic and two immunoblastic lymphomas). These results confirm previous reports of the strong association of EBV with endemic BL, but suggest that the virus is not important in the pathogenesis of other types of African high-grade B cell lymphoma from regions where BL is endemic.

Primary central nervous system lymphomas--an update

Primary CNS lymphomas (PCNSL), until recently representing about 1% of all brain tumors, show dramatically increased incidence both in high-risk groups (immunocompromised, AIDS) and in the general population. They are extranodal diffuse non-Hodgkin's lymphomas, the morphology and classification of which are identical to those of systemic lymphomas, although PCNSL show different biological behavior and diagnosis according to the New Working Formulation and updated Kiel classification may be difficult. The majority are large B cell variants of high-grade malignancy; low-grade subtypes and T cell lymphomas are rare. Sixty per cent occur in the supratentorial space (hemispheres, periventricular) and 12% in the posterior fossa; 30% are multiple (50%-70% in AIDS). PCNSL show a male preponderance with a peak incidence in the 5th-7th decade (3rd-4th in AIDS). The duration of diffuse or focal clinical symptoms averages 1-2 months. Computed tomography and magnetic resonance imaging scans show single or multiple or diffuse, often typical lesions. Diagnosis is achieved by evaluation of stereotactic biopsy material or cerebrospinal fluid cytology using immunocytological markers. Current therapy in immunocompetent patients, radiation plus corticosteroids and pre- or postradiation polychemotherapy, shows response rates of 85% with a median survival of 17-44 months, a prognosis similar to that for glioblastoma. Meningeal PCNSL is treated with intrathecal methotrexate or cytosine arabinoside. Transliquoral seeding of PCNSL is frequent, distant metastases occurring in 6%-8%. Therapy of AIDS-related PCNSL makes use of radiation and corticosteroids, and rarely of chemotherapy. The pathogenesis of PCNSL is unknown, but Epstein-Barr virus may be a contributory factor.

Detection of Epstein-Barr virus genomes in AIDS related lymphomas: sensitivity and specificity of in situ hybridisation compared with Southern blotting

Eighteen cases of AIDS related, non-Hodgkin's lymphomas were examined for the presence of Epstein-Barr virus (EBV) genomes using in situ hybridisation with a 35S-labelled probe. The results were compared with those obtained independently by Southern blot analysis with a 32P-labelled probe of frozen tissue from the same tumours. Technically satisfactory results were obtained with both methods in 15 lymphomas. EBV DNA was detected in seven of 15 (47%) cases by in situ hybridisation and in eight of 15 (53%) cases by Southern blotting (including all the cases positive by in situ hybridisation). The results of EBV DNA detection by the two techniques were identical in 14 of 15 (93%) cases. In situ hybridisation gave no false positive results. This study shows that the sensitivity and specificity of in situ hybridisation for the detection of EBV genomes in AIDS related lymphomas approaches that of Southern blotting, even when using routinely processed archival, paraffin wax embedded material.

Detection of single copies of Epstein-Barr virus in paraffin wax sections by non-radioactive in situ hybridisation

A highly sensitive non-isotopic in situ hybridisation technique was developed for the localisation of Epstein-Barr virus (EBV) in paraffin wax embedded tissue sections. The method uses a repeated sequence of the EBV genome as a probe, labelled with the novel reporter molecule, digoxigenin. The method can identify individual copies of EBV by detection of both EBV DNA and highly localised RNA transcripts. A combination of careful proteolytic digestion of tissue sections, high temperature denaturation of probe and target DNA, and sensitive immunocytochemical detection are used to attain single copy sensitivity. The technique is quicker and simpler to perform than some other methods used for the identification of EBV, and provides simultaneous morphological information which cannot be obtained by methods using tissue extracts. This method permits the investigation of the role of EBV in neoplastic conditions of lymphoid and epithelial cells, and may prove valuable in determining the sites of latent virus in healthy subjects.

What's new in primary central nervous system lymphomas?

Primary central nervous system lymphomas (CNSL) are uncommon neoplasms accounting for about 1% of primary brain tumors. Patients with congenital or acquired immunodeficiencies including AIDS patients and transplant recipients represent the main high-risk population for CNSL occurrence. An important point emerging from the literature is that CNSL incidence has dramatically increased during the last years not only in HIV infected patients by virtue of the AIDS epidemic spread, but also for unclear reasons in immunologically normal persons. Although c-myc oncogene activation and Epstein-Barr virus infection are considered to play a role in CNSL development, the peculiar tendency of these lymphomas to occur and remain inside the CNS is not well understood and may involve putative CNS binding molecules carried by lymphocytes. The clinical presentation is characterized by a great variety of neurological disorders. Radiological features consist of hyperdense homogeneous deposits within the subcortical white matter with a pattern of marked enhancement after injection of contrast material. The tumor masses are usually ill-defined and multicentric. Although all cytological types can be observed, the most common types belong to the high-grade category of non-Hodgkin's lymphoma. Monoclonal antibodies reactive with formalin-fixed, paraffin-embedded sections can be used in conjunction with stereotactic needle biopsy to provide accurate immunological characterization of CNSL. The large majority of CNSL is of B-cell origin but T-cell lymphomas seem at the present time less exceptional than previously thought. Although radiotherapy and chemotherapy can increase length of survival, the prognosis of CNS remains dramatically poor, the shortest survival being observed in AIDS patients.