Mycobacterial spindle cell pseudotumors (MSPs) are a rare and diagnostically challenging manifestation of non-tuberculous mycobacterial (NTM) infections. Proper recognition of these pseudotumors is important because they are treatable and benign. In this study, we evaluated the morphologic patterns of MSPs to improve their pathologic identification. Clinical and morphologic features of 14 MSPs were analyzed. Histologic factors evaluated included the architectural growth pattern of spindled or epithelioid macrophages, granulomas and their location within the lesion, neutrophilic microabscesses, multinucleated giant cells, necrosis, and effacement of background tissue. The composition of inflammatory infiltrates, organism density by acid-fast staining, and stromal changes were also assessed. In addition, 8 of 14 cases underwent molecular microbiology identification by a clinical amplicon-sequencing assay for non-tuberculous mycobacteria. MSP sites included 2 bowel, 10 lymph nodes, 1 liver, and 1 extremity. Cases with available clinical history (n=10) all occurred in immunocompromised patients. All demonstrated effacement of normal structures with spindled cells arranged in a storiform or fascicular architectural pattern. In addition, all cases showed lymphocytic inflammation, with prominent concurrent neutrophilic inflammation in 50% (7/14) of cases. Other morphologic findings included foamy histiocytes (64%, 9/14), peripherally situated granulomas (21%, 3/14), and neutrophilic microabscesses (21%, 3/14). All tested cases were positive for NTM by PCR methods. Mycobacterium avium was the most commonly isolated pathogen (6/8). Mycobacterial spindle cell pseudotumors show predominantly spindled morphology that may be mistaken as a neoplasm. Surgical pathologists who evaluate lymph nodes, soft tissue, and gastrointestinal tissues should be aware of this spindled tumefactive phenomenon in the setting of immunocompromised patients. Recognition of key morphologic features of neutrophilic inflammation, peripheral granulomas, or foamy histiocytes within a spindled lesion can help guide the pathologist to a correct diagnosis of an inflammatory process secondary to infection rather than a spindle cell neoplasm. Accurate diagnosis to facilitate appropriate antimicrobial and/or surgical therapy requires a comprehensive evaluation combining clinical, histopathologic, and microbiological findings.

中文翻译：

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分枝杆菌梭形细胞假瘤的组织学特征：14 例多机构临床病理分析。


分枝杆菌梭形细胞假瘤 (MSP) 是非结核分枝杆菌 (NTM) 感染的一种罕见且诊断上具有挑战性的表现。正确识别这些假瘤很重要，因为它们是可治疗的且是良性的。在这项研究中，我们评估了 MSP 的形态模式，以提高其病理学识别能力。分析了 14 个 MSP 的临床和形态学特征。评估的组织学因素包括梭形或上皮样巨噬细胞的结构生长模式、肉芽肿及其在病变内的位置、中性粒细胞微脓肿、多核巨细胞、坏死和背景组织的消失。还评估了炎症浸润的组成、抗酸染色的生物体密度以及基质变化。此外，14 例病例中的 8 例通过非结核分枝杆菌临床扩增子测序测定进行了分子微生物学鉴定。 MSP 部位包括 2 个肠道、10 个淋巴结、1 个肝脏和 1 个四肢。有可用临床病史的病例（n=10）均发生在免疫功能低下的患者中。所有这些都表现出正常结构的消失，梭形细胞排列成席纹状或束状结构图案。此外，所有病例均显示淋巴细胞炎症，其中50%（7/14）的病例伴有明显的中性粒细胞炎症。其他形态学发现包括泡沫状组织细胞（64%，9/14）、周围肉芽肿（21%，3/14）和中性粒细胞微脓肿（21%，3/14）。通过 PCR 方法，所有检测病例均呈 NTM 阳性。鸟分枝杆菌是最常见的分离病原体 (6/8)。分枝杆菌梭形细胞假瘤主要表现为梭形形态，可能被误认为是肿瘤。 评估淋巴结、软组织和胃肠组织的外科病理学家应该意识到免疫功能低下患者中这种梭形肿胀现象。识别梭形病变内的中性粒细胞性炎症、外周肉芽肿或泡沫状组织细胞的关键形态学特征，有助于指导病理学家正确诊断继发于感染的炎症过程，而不是梭形细胞肿瘤。为了促进适当的抗菌和/或手术治疗，准确的诊断需要结合临床、组织病理学和微生物学发现进行综合评估。