| | Mediastinal granuloma | Fibrosing mediastinitis |
| Etiology | - Prior Histoplasma infection.*
- Old mycobacterial tuberculosis infection.
- Sarcoidosis.
| - Remote Histoplasma infection.*
- Old mycobacterial tuberculosis infection.
- Other infection (eg, Aspergillus, Wuchereria, Blastomyces, Actinomyces, and Treponema).
- Other – Sarcoidosis, IgG4-related diseases, autoimmune vasculitis, radiation, Methysergide, silicosis.
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| Clinical presentation | - Asymptomatic presentation is common.
- Symptoms of mediastinal compression or fistulization:
- Compression is most commonly of the SVC, esophagus, or lower airway
- Fistulization is most commonly to the esophagus or lower airways, rarely to the pericardium
| - Asymptomatic presentation is usual but symptoms develop with disease progression.
- Symptoms of mediastinal compression (vascular, in particular the pulmonary artery and veins, SVC, and airway are the most common). Hemoptysis is one of the most common features (due to bronchial artery hypertrophy and bleeding). Symptoms of post-obstructive pneumonia also common. Fistulization does not occur.
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| Chest CT | - Well-defined mediastinal mass (or conglomerate lesions) with rim-enhancing, scattered or diffuse calcifications and a heterogenous density.
- Evidence of prior Histoplasma infection (eg, calcified lymph nodes and hepatic or splenic calcifications).
- Extrinsic compression that is not circumferential.
- Fistulization may be present.
| - Ill-defined but dense mediastinal infiltrate that obliterates fat planes, contains calcifications and has a heterogenous density. The infiltrate is more commonly unilateral than bilateral, and mostly right-sided.¶
- Evidence of prior Histoplasma infection (eg, calcified lymph nodes and hepatic or splenic calcifications).
- Extrinsic compression that is often circumferential.
- Fistulization absent.
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| Diagnosis | - Classic CT appearance – common, diagnostic in endemic regions.
- Need for tissue biopsy – infrequent; needle aspiration and biopsy risk rupture and spillage of contents into the mediastinum and may also result in bacterial superinfection. Biopsy may be necessary in atypical cases (eg, absent calcification) to rule out malignancy.
| - Classic CT appearance – common, diagnostic in endemic regions.
- Need for tissue biopsy – not indicated in setting of classical CT appearance including calcifications. Biopsy should be pursued in the absence of classical imaging to rule out malignancy or alternative etiology. Biopsy can be fraught with difficulties, including hemorrhage from collateral vessels.
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| Prognosis | - Good. Many cases resolve or never become symptomatic. Fistula formation can lead to life-threatening complications including retrograde bacterial superinfection from esophageal fistulization or pericardial tamponade from pericardial fistulization. Surgical resection can be curative.
| - Generally progressive disease. Unilateral disease is not typically life-threatening, though may lead to unilateral pulmonary artery auto-amputation. Bilateral disease may be life-threatening. Treatment with vascular or airway stenting may preserve some function.
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