Pulmonary Mycobacterial Spindle Cell Pseudotumor: A Report of 3 Cases Including a Practical Approach to Histopathologic Recognition of This Unusual Entity

Abstract

Mycobacterial spindle cell pseudotumor (MSP) is a rare benign spindle cell lesion containing acid-fact mycobacteria. These lesions are most commonly identified in the lymph nodes, skin, spleen, or bone marrow of immunocompromised patients and only rarely involve the lungs. We report 3 cases of pulmonary MSP, which include 2 patients who are known to be HIV-positive. The histopathological diagnosis of MSP in the lung lends itself to many challenges due to its rare incidence and its spindled tumor-like appearance. The differential diagnosis is broad and includes both benign and malignant entities. We highlight the importance of the clinical context in which these lesions typically present and the morphologic spectrum of features seen, and we offer a practical approach to the workup of pulmonary mycobacterial pseudotumor. Appropriate recognition of this entity should lead to an accurate diagnosis of a treatable benign condition despite the clinical presentation often favoring malignancy.

Mycobacterium Spindle Cell Pseudotumor Caused by Mycobacterium xenopi: A First Described Association of a Rare Entity Presenting in the Lung

“…14 The increased prevalence of NTM seems to coincide with more widespread use of immunosuppressive drugs, particularly the newer biologic agents that inhibit tumor necrosis factor-α such as infliximab, etanercept, and adalimumab. 15…”

“…MSP shares close pathologic features to certain neoplasms, in particular, Kaposi sarcoma (KS), sarcomatoid carcinoma, spindle cell melanoma, inflammatory myofibroblastic pseudotumor, primary neurogenic tumors, and well-differentiated neuroendocrine tumor. 15,16 The most helpful feature in MSP is its vaguely granulomatous appearance, which should prompt the pathologist to request special stains, for example, GMS, Fite’s stain, and periodic acid stain; however, this vaguely granulomatous appearance may be subtle and easily missed. 15…”

“…15,16 The most helpful feature in MSP is its vaguely granulomatous appearance, which should prompt the pathologist to request special stains, for example, GMS, Fite’s stain, and periodic acid stain; however, this vaguely granulomatous appearance may be subtle and easily missed. 15…”

Laryngeal Inflammatory Pseudotumour Secondary to Mycobacterium kansasii

“…It is also the commonest nontuberculous mycobacterium causing pulmonary infection in the UK [ 11 ]. IPT associated with mycobacterial disease has been reported in skin [ 12 ], lymph nodes [ 13 ], lung [ 14 , 15 ], brain [ 16 ], and sinuses [ 17 ]. There have been cases of head and neck manifestations of IPT reported in lymph nodes, parotid, the para-pharyngeal space [ 18 ], and the tonsil [ 19 ].…”

Laryngeal inflammatory pseudo-tumour secondary to mycobacterium kansasii

“…It is also the commonest nontuberculous mycobacterium causing pulmonary infection in the UK [11]. IPT associated with mycobacterial disease has been reported in skin [12], lymph nodes [13], lung [14,15], brain [16], and sinuses [17]. There have been cases of head and neck manifestations of IPT reported in lymph nodes, parotid, the para-pharyngeal space [18], and the tonsil [19].…”