Correct!
4. MALT lymphoma

The history of MALT lymphoma combined with the exudative pleural effusion and the atypical lymphocytic cytology make this the most likely diagnosis. Congestive heart failure should present with a transudative effusion and an effusion this large limited to the right chest would be unusual. Empyema should present with a neutrophilic predominant effusion and metastatic carcinoma of the lung should present with compatible cytology showing cancer cells in the pleural fluid.

Although mucosa associated lymphoid tissue (MALT) lymphoma represents the most common type of primary pulmonary lymphoma (PPL), PPLs only make up 0.5% of primary lung malignancies (2). Pulmonary MALT lymphomas most commonly presents with either non-specific symptoms or asymptomatically. Patients are asymptomatic in 37-54% of cases (2,4,5), with discovery upon routine imaging (2,3).  Of those with symptoms, cough or exertional dyspnea are most common, in 21-46% (3-5). Weight loss occurs in 16-23% (3,4). 10-25% of patients have fever, pleuritic chest pain, fatigue, or hemoptysis (3,5).

Commonly reported radiographic features of pulmonary MALT lymphomas include focal lung nodules in 85-90% (2,3), with normal or dilated air bronchograms seen in 50-100% (2-6).  Both solitary and multifocal lesions are common, and bilateral involvement is seen in approximately 20% (3-6).  Other presentations include as round opacities (19-62%) (3-6), or as diffusely interstitial opacities (8%) (3). Mediastinal or hilar lymphadenopathy is reported in 15-25% (2-6).  Rarely, an associated pleural effusion is present, in 2-15% of reports (2-6).

Diagnosis requires confirmation by flow cytometry and/or cytology with immunohistochemistry on cell block specimen.  The immunohistochemistry aids differentiation of   MALT lymphoma from the other varieties of non-Hodgkin’s lymphoma (2).  MALT lymphomas generally follow an indolent course, and survival at five years is 93% (2). 

This case of pulmonary MALT lymphoma causing a unilateral pleural effusion is unusual. Most pulmonary MALT lymphomas are clinically asymptomatic and radiographically nonspecific.  Thus, consideration of pulmonary MALT lymphoma is appropriate when faced with nonspecific symptoms and a variety of chest imaging findings.

Acknowledgments

Carr, Gordon MD. Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, University of Arizona, Tucson, AZ

References

1. Galgiani JN, Ampel NM, Blair JE, et al. 2016 Infectious Diseases Society of America (IDSA) clinical practice guideline for the treatment of coccidioidomycosis. Clin Infect Dis. 2016 Sep 15;63(6):e112-46. [CrossRef] [PubMed]
2. Cardenas-Garcia J, Talwar A, Shah R, Fein A. Update in primary pulmonary lymphomas. Curr Opin Pulm Med. 2015 Jul;21(4):333-7. [CrossRef] [PubMed]
3. Cordier JF, Chailleux E, Lauque D, et al. Primary pulmonary lymphomas. A clinical study of 70 cases in nonimmunocompromised patients. Chest. 1993 Jan;103(1):201-8. [CrossRef] [PubMed]
4. Huang H, Lu ZW, Jiang CG, Li J, Xu K, Xu ZJ. Clinical and prognostic characteristics of pulmonary mucosa-associated lymphoid tissue lymphoma: a retrospective analysis of 23 cases in a Chinese population. Chin Med J (Engl). 2011 Apr;124(7):1026-30.  [PubMed]
5. Sui X, Song W, Jin ZY, Feng RE, Cui QC, Xue HD, Li S, Sun H. Clinical and imaging manifestations of pulmonary mucosa-associated lymphoid tissue lymphoma. Zhongguo Yi Xue Ke Xue Yuan Xue Bao. 2012 Feb;34(1):41-5. [PubMed]
6. Qiang J, Qi PF, Gao WQ, Chen DS, Yü W. Imaging findings of non-contrast CT scan, enhancement and HRCT of pulmonary mucosa-associated lymphoid tissue lymphoma. Zhonghua Yi Xue Za Zhi. 2013 Jun 4;93(21):1634-6. [PubMed]

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