**4.3 Pulmonary nodules**

*Pulmonary nodules* (see **Figure 5**) from histoplasmosis are frequently detected incidentally, most of them representing the primary healed granulomatous lesion. Histoplasmosis is actually the most common cause of non-cancerous granulomatous nodules and masses in endemic regions [13].

More often, additional investigations are necessary to establish a diagnosis of certainty; the differential diagnosis is made mainly with nodules of malignant etiology; these lesions can mimic bronchopulmonary neoplasm or lung metastases. The differential diagnosis may require the performance of PET CT with 18F-FDG (fluorodeoxyglucose), which will highlight in the subacute phase of the infection lung nodules or masses with a faster reduction of affinity for 18F-FDG compared to associated adenopathies in contrast to proliferative lesions-malignant. Thus, in smoking or ex-smoking patients with nodules over 1 cm, it is necessary to perform a biopsy, either by transthoracic biopsy with a fine needle or by surgical excision. In the case of subcentrimetric nodules, imaging monitoring is recommended. Anti-Histoplasma

### **Figure 5.**

*CT images in the axial plane: (left) solitary pulmonary tissue nodule located in the periphery of the right lower lobe, with central calcification—pathognomonic appearance for histoplasmoma; (right) nodular appearance evident on the lung window.*

antibodies can be detected in some patients, but the titers are usually low (1:8–1:16), and antigen tests are mostly negative. In the histopathological examination, both casefied and non-casefied granulomas can be detected. Cultures, even on special media for fungi, are often negative because the organisms are not viable [14, 15].

The *histoplasmoma* represents the solitary healed nodular lesion, with central calcification determining the appearance of a "target" lesion, pathognomonic for histoplasmosis (see **Figure 6**) [16].
