Findings: There is a very large (~10×30 cm), complex, heterogenous retroperitoneal mass which surrounds, but does not invade, the aorta and extends from the level of the caudal pole of the kidneys to the pelvic inlet. This mass is cavitated with variably sized pockets of echogenic fluid. Some of these pockets of fluid appear to have thick, echogenic walls. The mass is mildly vascular. There is a smaller, cavitated mass caudal to the right kidney which may be a separate retroperitoneal mass or a pedunculated section of the large mass. There is a scant amount of anechoic retroperitoneal fluid. The hypaxial muscles and ventral vertebral column appear within normal limits. Bilaterally the renal cortices are hyperechoic with decreased corticomedullary distinction. There is pyelectasia and blunting of the renal papillae, right worse than left. The ureters are not dilated but have slightly thickened walls.

Conclusion: Large retroperitoneal mass may represent a large cavitated neoplasm (such as retroperitoneal sarcoma), or complex abscess or fungal granuloma. The appearance of the kidneys is indicative of current or previous pyelonephritis with ureteritis and mild chronic renal change. A component of the pyelectasia may also be secondary to obstruction by the retroperitoneal mass.

The patient underwent exploratory laparotomy. Due to the extent of the mass it was not excised but was debulked and numerous fluid-filled pockets were dissected and suctioned.

Retroperitoneal Mass: Marked, chronic, histiocytic, lymphoplasmacytic, and neutrophilic  inflammation with multinucleated giant cells, multifocal necrosis, with intralesional yeasts and hyphae.

The apparent fungal organisms in these sections were somewhat variable in morphology, and are qualitatively different from those described from cytologic impression smears. These rounded structures (apparent yeasts) were somewhat larger (15-30 micrometers in diameter), and the hyphal structures were generally broader (up to 10 micrometers wide) and often bulbous. A species-level identification was not possible based on the examined sections.

Given the partial fibrous capsule at the margin of this mass, and the presence of several medium-caliber arteries, we suspect that this mass might represent an effaced lymph node. Urine Aspergillus Antigen positive.