This is a 70-year-old patient who reported lower urinary tract symptoms in the form of an increase in nocturnal urinary frequency, slight dysuria and a slight decrease in voiding calibre.
Given these incipient prostate symptoms, he was referred to his local urologist, who performed a digital rectal examination (adenoma II), and requested a PSA determination and an abdominal ultrasound for the next consultation.
The patient's only previous history was an operation on the left eye as a result of trauma, and in urological terms, a ureterolitectomy of the upper third of the ureter 35 years ago in another centre, by means of a lumbotomy.
At the next consultation, and the patient being totally asymptomatic, an ultrasound examination revealed the existence of a parahilar mass in the left kidney of about 6 cm in diameter, a normal right kidney, a prostate of 35 cc, as well as a PSA within the normal range.
Given these findings and the suspicion of a renal tumour, a CT scan was performed with the result of a left parapapillary image, 5-6 cm in diameter, solid in appearance, extending from the renal hilum to below the lower pole, with compression of the kidney and with a dubious fatty plane of separation with the kidney, calcifications in its interior and very low vascularisation.

With the diagnosis of a renal mass, an extension study was performed, which was negative, and a surgical revision and excision of the mass and/or nephrectomy were considered, depending on the findings.
A fortnight later, a left lumbotomy was performed.
Once the renal dissection manoeuvres had begun, the mass was clearly identified as compressing the kidney, but with a clear plane of dissection between the two. Given the doubts as to the nature of the mass, an intraoperative biopsy was performed and textile fibres were obtained.
Given the evidence that it was a gauze from the previous operation, the entire tumour was excised, preserving the renal unit.
Once the mass had been excised, it was opened and fragments of one or several gauze fibres were found inside, with caseous material around them.

The anatomopathological analysis of the tumour wall showed hyaline material with a tendency to collagenisation, and an inflammatory reaction mainly due to histiocytes.
