Abstract Introduction Mediastinal granuloma and fibrosing mediastinitis are both rare sequalae of Histoplasma exposure. Differentiating between these is important because management and prognosis differs significantly. We report a case series of 3 patients each, seen between July 2024 and October 2025 to highlight differences between these conditions. Discussion Differentiating features observed between these two conditions were - patients with mediastinal granuloma tended to have history of exposure to marijuana, presence of fistulization on imaging, and absence of pleural effusion. Symptoms tended to be acute or subacute in mediastinal granuloma patients and chronic in fibrosing mediastinitis patients. This abstract is funded by: None Case Descriptions Patients with mediastinal granuloma were younger (ages 21, 29 and 31) and presented with acute dyspnea, productive cough and fever with symptom duration varying from 1-4 weeks. All patients had a history of vaping/smoking tobacco and marijuana. Imaging showed large subcarinal lympadenopathy with calcifications with compression of distal bronchi in all patients. 2 patients also had hilar lympadenopathy (Station 11Ri). All patients had concern for fistulization (presence of gas bubbles inside the mediastinal lesion) and same was confirmed in 2 patients (visualized in OR / on barium swallow). All patients underwent bronchoscopic biopsy with EBUS and infectious work up. Pathology showed histiocytic aggregates with granulomas and giant cells suggesting acute on chronic inflammation. Cultures only grew oral bacteria (Alpha streptococcus or Gemella morbillorum). Only 1 patient tested positive for Histoplasma antibodies (M band). One patient had to be referred to a higher center for granuloma resection and fistula repair due to severe dysphagia/dyspnea from mass effect. The other two felt better with antibiotic (not antifungal) therapy. Follow up imaging was available for one patient which showed reduction in size of granuloma (which had fistulized). Patients with fibrosing mediastinitis were older (44, 48 and 54). They presented with dyspnea without fever for weeks to months. None of them had history of marijuana use. Imaging showed calcified lymphadenopathy in addition to encasement of pulmonary arteries / veins and pleural effusion on the same side. One patient also had evidence of retroperitoneal fibrosis on imaging. Workup again showed negative fungal antibodies (though one patient had Histoplasma visualized on a lymph node sample via mediastinoscopy). Pathology showed histiocytes and granulomas concerning for chronic inflammation. One patient’s pleural effusion was large enough to be sampled - analysis showed a transudative effusion with lymphocyte predominance. Surprisingly, all patients reported here were African American.
Kushwaha et al. (Fri,) studied this question.