61 Histoplasmosis

Clinical Presentation

Asymptomatic 30-year-old woman evaluated for an enlarging lung lesion

Radiologic Findings

PA chest radiograph (Fig. 61.1A) demonstrates a multi-lobulated left lower lobe nodule and ipsilateral calcified hilar lymph nodes. Contrast-enhanced chest CT (mediastinal and lung windows) (Figs. 61.1B, 61.1C, 61.1D) demonstrates clustered non-enhancing left lower lobe nodules with intrinsic round calcifications. The clustered nature of the lesions is best visualized on the coronal reformatted CT image (Fig. 61.1D).

Diagnosis

Histoplasmosis

Fig. 61.1

Differential Diagnosis

• Granulomas; Other Fungal Infections

• Granulomas; Tuberculosis

Discussion

Background

Histoplasmosis is a fungal infection endemic to the south-central United States, especially the Mississippi and Ohio River valleys.

Etiology

Histoplasmosis is caused by Histoplasma capsulatum, a dimorphic fungus transmitted through inhalation of airborne spores typically released from infected soil enriched by bird droppings or guano. Inhaled organisms multiply within macrophages and undergo lymphatic and hematogenous dissemination. Cellular immunity develops within two weeks, with subsequent healing.