Male patient, 68 years old, former textile industry worker, referred for consultation due to complex renal cystic mass. History of rheumatoid arthritis, controlled hypertension, dyslipidaemia, pulmonary tuberculosis 40 years ago, medicated with indapamide, sinvastatin and NSAIDs. He denied smoking habits or exposure to chemical agents. He reported exposure to sheep in his youth. He denied a known history of renal lithiasis. He had undergone left hip arthroplasty years ago. No history of abdominal or genitourinary surgery. For months he reported elimination of gelatinous material in the urine, with no specific shape, accompanied by episodes of total macroscopic haematuria, without clots. No other accompanying symptoms, such as back pain, nausea or vomiting, or lower urinary complaints. No anorexia, asthenia or weight loss. No respiratory or gastrointestinal symptoms.
On physical examination there was a non-painful left flank/lumbar emplasia. No hepatomegaly, no abnormal abdominal collateral circulation. Genitalia without clinical varicocele. Lower limbs without oedema. No peripheral adenopathies. Pulmonary auscultation without apparent alterations.
In analytical terms he had mild anaemia (Hb 12.7 g/dL), without leukocytosis. Relative eosinophilia (2800/µL). SV 67 mm. Creatinine 1.2 mg/dL. Urea 77 mg/dL.
Ultrasonography revealed a right kidney of somewhat reduced dimensions (10.8 cm) and with increased echogenicity of the parenchyma, presenting a simple cyst in the upper pole. The left kidney showed a large complex cyst of the upper pole (70 x 68 x 67 mm), with evident solid content and associated regions with posterior acoustic shadowing. Subjected to abdominopelvic CT - voluminous complex cystic formation containing gross parietal and central calcifications, occupying the upper two thirds of the left kidney, as well as fine septa within it, presenting attenuation values varying between 10 and 20 Housefield units. Subsequent to contrast administration, there was evidence of contrast uptake by the walls. No lesions of solid abdominal organs, presence of retroperitoneal adenopathies or morphological alteration of the suprarenal glands were evident. Chest X-ray without significant alterations, such as cystic lesions or alterations compatible with lesions of metastatic nature or active tuberculosis. Negative Mantoux (tuberculin test). Acid-fast bacilli negative. Urine cultures (multiple samples) in Lowenstein's medium negative. Serology for Echinococcos granulosis and multilocularis negative.

With the diagnosis of Bosniak class IV complex cystic mass and in the absence of support for lesions of specific/parasitic infectious nature, he underwent left radical nephrectomy by lumbotomy incision over the 12th rib bed.
Pathological examination showed a neoplasm of 11.5 cm in greatest dimension, consisting of glands of simple and complex structure, the epithelium being moderately differentiated and centred by mucoid material in the form of large mucin pools with tumour fragments. The lesion invaded the renal parenchyma without affecting the capsule. The remaining parenchyma showed signs of pyelonephritis with mild atrophy. Surgical margins were free of tumour. Conclusion: mucinous adenocarcinoma of the renal pelvis PT3NxMx.

After histological results were available, the patient underwent upper endoscopy and colonoscopy, which showed no alterations.
He was followed up for 10 months. The patient is totally asymptomatic and there is no evidence of recurrence of the disease, locally or at a distance.