Vesical fungus ball

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Fungal balls of the urinary tract, also known as fungal bezoars or mycetomas of the urinary tract, are a rare manifestation of funguria, usually candiduria.

Epidemiology

While candiduria may be seen in approximately 20% of hospitalized patients , development of fungal balls is considered very uncommon, although the exact incidence is unknown. They are more commonly seen in the neonatal and elderly demographics .

Risk factors

Fungal balls are generally seen in the presence of at least one of the following :

  • diabetes mellitus
  • immunocompromised state (e.g. post-transplant patients, HIV with poor virological suppression)
  • indwelling catheterization
  • anatomical urinary tract anomalies
  • urinary retention (e.g. bladder obstruction, neurogenic bladder)
  • prolonged antibiotic therapy
  • concurrent malignancy

Clinical presentation

Fungal balls of the urinary tract are usually diagnosed in the context of a symptomatic urinary tract infection or urosepsis, and are not symptomatic themselves unless they cause obstruction . If obstructive, they may contribute to renal colic-type pain, development of or worsening of pyelonephritis, and a post-renal acute kidney injury .

Pathology

Etiology

The etiology of fungal balls is not clearly understood, however they are thought to be an agglutination of :

The most commonly implicated pathogen is Candida albicans, however many other fungal isolates have been described in the literature, including other Candida spp., Aspergillus spp., Rhizopus oryzae, and Geotrichum candidum .

Location

Fungal balls can exist anywhere along the urinary tract, however are most commonly described as existing within the renal pelvis .

Radiographic features

Fungal balls are often seen in the setting of cystitis, pyelonephritis, papillary necrosis, and/or evidence of urinary tract obstruction (e.g. hydronephrosis, hydroureter) .

Plain radiograph

Plain radiography is often unremarkable, however unusual locules of gas or calcification may be seen within the urinary system possibly indicative of underlying fungal ball .

Fluoroscopy

Cystography and pyelography may reveal contrast filling defects where the fungal balls lie .

Ultrasound

Generally, fungal balls are appreciated as mobile, rounded, heterogeneously hypoechoic masses, although hyperechoic masses have also less frequently been described . No evidence of vascularity is seen within the mass on a Doppler study .

CT

Fungal balls have a heterogeneous soft-tissue density on CT without contrast-enhancement, but may also have regions of gas or calcification . They are rounded and not attached to the walls of the urinary tract, with a thin rim of urine often appreciable around the mass . CT urography (e.g. CT intravenous pyelogram) reveals filling defects, similar to fluoroscopy .

MRI

Morphological findings are identical to those seen on CT . Signal characteristics of fungal balls have been rarely described, but include :

  • T1: isointense to renal parenchyma
  • T2: hyperintense to renal parenchyma

Similar to other modalities, MR urography reveals filling defects .

Treatment and prognosis

Treatment is typically with local and/or systemic antifungal therapy, such as fluconazole or amphotericin B . If refractory to pharmacotherapy, fungal balls may be surgically removed .

Differential diagnosis

Depending on the modality, the following may be considered: