renal cell carcinoma is the most common solid tumour occurring within the kidney representing 2 - 3% of cancers diagnosed . ( 1 ) renal ectopia is also not uncommon and is found in 1 of 2100 to 3000 autopsies ( 2 ) ; however the incidence of renal cell carcinoma in a pelvic kidney is rare , and has only been described in a very small number of cases . ( 3,4,5 ) we describe a case where an incidental ectopic kidney with invasive renal cell carcinoma was diagnosed during an emergency admission . a 55 year old gentleman with a background history of posterior cortical atrophy ( pca ) presented with acute urinary retention . he had recently been discharged from a two week respite stay where his wife had noticed one stone of weight loss . he was catheterised and referred onto the admitting surgical team due to high urinary residuals ( > 1500mls ) . this gentleman was constipated but apart from the short history of weight loss and abdominal pain relating to retention , he had no other symptoms . he was haemodynamically stable , with a mild normocytic anaemia ( haemoglobin 12.5g / dl ) . his urine microscopy subsequently revealed white cells between 10 - 10 cells / litre and urine red blood cells > 10 cells / litre . on abdominal examination , there was a mass palpable in the left iliac fossa , which was initially thought to be an intra - abdominal malignancy and therefore a computed tomography ( ct ) scan of the abdomen and pelvis was arranged . this demonstrated a normal right kidney , absence of a normally positioned left kidney and a complex solid lobulated 11 x 7 cm mass arising from a presumed left pelvic kidney ( figure 1 ) . coronal image showing a reniform mass in the central pelvis : a presumed left pelvic kidney with a complex heterogenous mass arising and extending inferiorly . the patient was discharged home with catheter in situ . following review in the urological outpatient clinic , due to the nature of the patient s background , the family and clinical team felt that operative management would not be in his best interests and therefore symptomatic management was decided upon . a post mortem carried out found a left pelvic kidney infiltrated with a 12 cm renal cell carcinoma within the lower pole , with no metastases . renal ectopia occurs due to mal - ascent of the kidney to the renal fossa . autopsy series have shown an incidence of the range 1 of 2100 to 3000 autopsies . ( 1 ) most pelvic kidneys are asymptomatic , and there is not thought to be an increased susceptibility to disease . renal cell carcinoma in a pelvic kidney is extremely rare and has only been documented in a few other cases . most cases documented presented with chronic abdominal pain with the pelvic kidney found on ultrasound scan and one case presented with painless haematuria . ( 4 ) our case is the only case documented that was diagnosed whilst presenting with acute urinary retention . this provided an opportunity for a thorough abdominal examination and therefore the abdominal mass was palpated . this case highlights the importance of always performing a full and thorough assessment of a patient , even when they are presenting with a common condition .
the incidence of renal cell carcinoma in a pelvic kidney is rare , and has only been described in a very small number of cases . 
 we describe a case where an incidental ectopic kidney with invasive renal cell carcinoma was diagnosed during a separate emergency admission for acute urinary retention .