Fungus ball, renal

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Fungus ball, renal,

the result of fungal infection of the kidney, which usually occurs

as an opportunistic infection in the immunocompromised patient

(through AIDS, transplant or chemotherapy) and in patients with

diabetes, on long-term antibiotics, or with indwelling intravenous or

urinary catheters.

Fungal infections may also occur as a secondary infection in the

setting of Gram-negative bacterial infections. The most common

organism is Candida albicans or other candidal species.

Other fungi include: Coccidiomycosis immitis, Cryptococcus

neoformans, Torulopsis glabrata and Aspergillus fumigatus.

Candidal infection of the kidneys may occur as the result of systemic

candidiasis or primary renal candidiasis. In systemic candidiasis,

the fungus is disseminated to the kidneys haematogenously. Multiple

organs such as the brain and the lungs may also be involved. Systemic

candidiasis is a fatal infection if not treated promptly. Primary

renal candidiasis occurs without haematogenous dissemination or

involvement of other major organs. Pathogenetically, it is thought to

result from a milder, more limited from of haematogenous spread.

Alternatively, the role of ascending infection from the lower urinary

tract has been proposed. Primary renal candidiasis is most commonly

seen in diabetic women.

Pathologically, fungi which are filtered by the glomeruli become

lodged in the distal tubules, where they proliferate and produce

microabscesses. Papillary necrosis ensues as the fungi infiltrate the

tips of the renal papillae. The fungi are then extruded into the

renal collecting system, resulting in fungus balls (mycetomas). The

fungus balls may cause obstruction, resulting in hydronephrosis, pain

and even renal failure if severe and long-standing.

Fungal infection of the kidneys can be diagnosed through

demonstrating fungal hyphae in urine. On excretory radiography, the

fungus balls are seen as multiple filling defects of between 1 and 4

cm within the collecting system. Associated radiological findings

include diminished excretion of contrast, papillary necrosis,

hydronephrosis. Sonographically, the fungus balls are seen as

hyperechoic masses without acoustic shadowing. On CT, they are low-

density lesions. CT is the preferred imaging modality for evaluating

fungal balls in the kidney and for fungal pyelonephritis in general.

It can accurately depict morphological lesions, functional

abnormalities in contrast uptake and excretion, and associated

complications such as perinephric abscess.

Treatment includes systemic antifungal therapy. Direct removal of the

fungus balls through percutaneous nephrostomy has been employed as

adjuvant therapy. See mycetoma renal

HH

The Encyclopaedia of Medical Imaging Volume IV:2