FINAL DIAGNOSIS: PRIMARY MALT LYMPHOMA OF DURA
Since first description of primary low grade B cell lymphoma of mucosa associated lymphoid tissue (MALT) involving the gastrointestinal tract by Isaacson and Wright in 1984 (4), it has become apparent that MALT lymphomas arise in wide variety of extranodal sites (2, 3). MALT lymphoma represents a unique clinicopathological entity distinguished by indolent clinical behavior and tendency to spread to non-contagious mucosa associated sites. Dural low-grade B cell lymphoma of MALT type was first described by Kumar et al. in 1997 (7).
Histological hallmarks of MALT-type lymphoma are: i. Polymorphous infiltrate with predominant small, centrocyte-like lymphoid cells, characterized by irregular nuclear membrane, of which CD20 and/or CD79a positive. ii. Presence of interspersed reactive T cells with no atypia. iii. Lymphoid follicles may be seen, but usually immature or poorly formed. iv. Plasmacytoid differentiation or numerous plasma cells are frequently seen. v. Light chain restriction may be present and helps in distinguishing from reactive lymphoid proliferation but not obligatory for the diagnosis. vi. CD5 and CD10 are negative, whilst small lymphocytic lymphoma or chronic lymphoid leukemia (SLL/CLL) is CD5 positive. Extranodal lymphomas in general that remain localized to primary site for a long time are more common in women, however, small lymphocytic lymphoma, CLL and plasmacytoid lymphoma are more frequent in men and tend to be disseminated usually even at the time of the diagnosis. Therefore, the diagnosis of meningeal MALT-type lymphoma requires exclusion of a disseminated lymphoma.
MALT lymphoma is rare but recognized subtype of primary meningeal lymphoma. To date 7 cases of MALT lymphomas of dural origin have been published (7, 5). There is only one reported case of leptomeningeal low-grade B cell marginal zone lymphoma showing typical MALT features (6), although Isaacson has seen a few (unreported) MALT-type lymphomas in leptomeningeal location [Isaacson, personal communication]. There might be other unreported or unrecognized meningeal MALT lymphomas published in the literature, diagnosed as plasmacytoid lymphoma, dural plasmacytoma and Castleman's disease of the dura. All reported meningeal MALT lymphomas, including our case, occur in women of middle age. Majority of these cases presented with a lesion in the dura radiologically mimicking menigioma or subdural hematoma. All reported MALT lymphomas of dura were relatively indolent, with excellent prognosis after surgical excision and with or without chemo- or radiotherapy. Our patient appears to be fully recovered after complete resection of the tumor.
Extranodal MALT lymphomas are thought to occur following transformation of a chronic lymphocytic inflammation due to infections or autoimmun diseases, like for instance Helicobacter pylori infection of stomach and Sjogren's syndrome of the salivary glands (1, 3). It is possible that meningeal MALT-type lymphomas may also follow on from a pre-existing inflammatory process, however there is no direct evidence to support this.
We would like to thank to Professor Peter G Isaacson in University College of London for reviewing this case.
Contributed by István Bódi, Ahmed Hussain, Richard W Gullan and Safa Al-Sarraj