The most common extraintestinal manifestations of Crohn's disease involve the eyes, skin, and the hepatobiliary, musculoskeletal and respiratory systems. These include conditions such as uveitis, episcleritis, erythema nodosum, pyoderma gangrenosum, sclerosing cholangitis, sacroilitis and organizing pneumonia. Mass-forming granulomatous inflammation in extraintestinal organs is extremely rare, with only a few recent reports of patients with Crohn's disease presenting with inflammatory pseudotumours in the liver, pancreas and kidneys. We present a case of mass-forming renal granulomatous inflammation in a patient with Crohn's disease. A 31-year-old female was diagnosed with Crohn's disease based on characteristic clinical features, and colonoscopy and histology of small and large bowel demonstrating non-caseating granulomas. She had undergone an ileocolic resection in 2009, following which she was treated with azathioprine and intermittent prednisolone.
MRI was performed in February 2012 for investigation of a 2-week history of abdominal pain and diarrhoea, demonstrating active enterocolitis and also revealing an incidental left renal mass that was a new finding since a CT scan of the abdomen performed in October 2011. The focal mass was located in the inferior pole of the left kidney and measured 2.5 x 2.9 x 2.3 cm; it had a lobulated margin and homogeneous signal, being slightly hypointense to the renal cortex on both T2 half-Fourier acquisition single-shot turbo spin-echo and true fast imaging with steady-state free precession images (Figure 1). The mass was isointense on pre-contrast T1 volumetric interpolated breath-hold examination and following contrast showed a honeycomb-type appearance with irregular enhancing septa around small non-enhancing elements that measured between 1 and 5 mm (Figure 1). The lesion had restricted diffusion and there was no abnormality within the perinephric fat or renal vessels (Figure 1). As the renal mass was an incidental finding on MRI focused on the small bowel, a dedicated contrast-enhanced renal CT scan was performed. On CT scan, the mass was isodense pre-contrast and homogeneously hypoenhancing in the arterial phase, while in the portal venous and delayed phases, it was hypoenhancing with cystic type non-enhancing foci within. No calcification or adenopathy was seen (Figure 2). Sonographically, the mass was slightly hypoechoic and had no demonstrable vascularity (Figure 3).
The differential diagnosis was focal pyelonephritis, including bacterial and mycobacterial aetiologies, renal neoplasm and inflammatory pseudotumour. A QuantiFERON Gold assay (an interferon-gamma release assay used as a diagnostic test for latent tuberculosis infection) was performed and a negative result was obtained. The patient had no prior history of tuberculosis or known tuberculosis contact, and multiple early morning urine cultures were negative. She received a short course of empiric intravenous antibiotics followed by oral amoxicillin/clavulanic acid. However, these were stopped, as the patient was clinically well. The lesion was stable on follow-up ultrasound imaging in May 2012 and this prompted an ultrasound-guided biopsy, providing histology that demonstrated a dense, mixed chronic inflammatory infiltrate with foci of granulomatous inflammation with focal necrosis. Some palisaded histiocytes with areas of necrosis were seen but there were no giant cells or polarizable foreign material present. Special stains for organisms, including periodic acid-Schiff and Ziehl-Neelsen, were negative and there were no features of malignancy (Figure 4). Mycobacterium tuberculosis polymerase chain reaction on tissue biopsy was negative. A tentative diagnosis of an inflammatory pseudotumour was made and a course of 30 mg daily of prednisolone was commenced, resulting in resolution of the lesion, with only a small focus of scar present on follow-up ultrasound and CT imaging performed in October 2012 (Figure 5). This response confirmed the diagnosis of inflammatory pseudotumour associated with Crohn's disease.