Primary Nocardia Infection Causing a Fluorodeoxyglucose-Avid Right Renal Mass in a Redo Lung Transplant Recipient

Abstract

Immunosuppression after lung transplantation may increase susceptibility to opportunistic infection and is associated with early and delayed deaths in lung transplant recipients. Factors that may predispose lung transplant recipients to opportunistic bacterial and fungal infections include prolonged corticosteroid use, renal impairment, treatment of acute rejection, and post-transplant diabetes mellitus. We present a unique case of a 63-year-old woman with diabetes mellitus who underwent redo lung transplantation. Three years after her right-sided single redo lung transplant, she presented with right-sided abdominal pain, nausea, and vomiting. Upon examination, computed tomography showed a 4.5 × 3.3 cm heterogeneous, enhancing right renal mass with a patent renal vein. Magnetic resonance imaging confirmed a T1/T2 hypointense, diffusion-restricting, right mid-renal mass that was fluorodeoxyglucose-avid on positron emission tomography. We initially suspected primary renal cell carcinoma. However, after a right nephrectomy, no evidence of neoplasia was observed; instead, a renal abscess containing filamentous bacteria was noted, raising suspicion for infection of the Nocardia species. Special stains confirmed a diagnosis of Nocardia renal abscess. Computed tomography of the chest and brain revealed no lesions consistent with infection. We initiated a long-term therapeutic regimen of anti-Nocardia therapy with imipenem and trimethoprim-sulfamethoxazole.

Figure 1

Computed tomogram of the abdomen-pelvis with contrast shows a 4.5 × 3.3 cm heterogeneous, enhancing soft-tissue density mass within the right kidney with a patent right renal vein (white arrow).

Figure 2

Positron emission tomography shows an intensely fluorodeoxyglucose-avid right renal mass with imaging characteristics highly suspicious for renal cell carcinoma (white arrow).

Figure 3

Renal mass pathology shows multiple renal abscesses with filamentous structures (red arrow) on hematoxylin and eosin stain under (a) low power (40x) and (b) high power (100x). Gomori's methenamine silver stain shows no fungal hyphae but highlights the filamentous bacterial forms (black arrow) under (c) low power (40x) and (d) high power (100x). These filamentous bacteria stain weakly positive with Fite's stain supporting the diagnosis of Nocardia species (yellow arrow) under low power (40x) (e) and high power (100x) (f).