Support Line: 0800 002 9002
General Enquiries: 01223 870008

Kidney Lumps

Kidney lumps are a common symptom of kidney cancer.

Kidney lumps/masses/lesions/tumours/growth

You may have been informed you have a lump/mass/suspicious lesion/ tumour or growth in your kidney.
This may have been picked up as an incidental finding whilst having a scan as part of another investigation.
A variety of tumours exist, and about 15% are benign. All kidney lesions require examination for malignant (cancerous) behaviour. (1)

Kidney Cysts

These may show up as a solid or cystic (watery fluid filled) lump.

Cystic masses

Cystic masses are categorised as simple or complex.
Simple cysts are very common in normal kidneys, with an increasing incidence as individuals age. These are benign (non- cancerous) and rarely cause complications or need treatment.
Complex cysts and small kidney masses less than 4cm in size are mostly benign. They may be due to infection, which may cause back pain, abdominal pain and fever. However, complex cysts have solid components and are more likely to be cancerous. If features look suspicious the radiologist will recommend follow up or further imaging for further clarification, such as ultrasound scan, magnetic resonance imaging (MRI) or contrast computed tomography (CT).

The Bosniak Classification of cystic masses (2)

Divides cystic masses into 5 categories based on imaging characteristics.
It is helpful in predicting a risk of malignancy (cancer) and suggesting either no follow up, follow up with imaging or treatment.

Bosniak 1 – Simple cyst- Non-malignant (not cancerous) 0 % percentage of malignancy, no follow up required
Bosniak 2 – Minimally Complex cyst – Non-malignant (not cancerous) 0 % percentage of malignancy. No follow up required
Bosniak 2F – 5% chance of malignancy. Imaging follow up required
Bosniak 3 – 54% chance of malignancy which will require intervention
Bosniak 4 -Solid mass with a large cystic or a necrotic component 100 % of malignancy (cancerous), which will require treatment.

Kidney Cancer

An actual kidney cancer diagnosis is determined by either further radiological imaging of CT or MRI. A kidney biopsy (small tissue sample of the lump/mass) may be used to obtain histology of radiologically indeterminate lumps/masses.
If a kidney cancer diagnosis is suspected or diagnosed, you will be seen by a urologist who will discuss further investigations or treatments most appropriate to you. These treatments may include nephrectomy (removing the whole kidney), Partial Nephrectomy (removing the lump in the kidney only and preserving the rest of the kidney) or renal ablation (cooking or freezing the lump).

Benign (non- cancerous) lumps/masses/lesions/tumours

Oncocytoma is the most common benign (non-cancerous) mass, however the imaging appearance of kidney cancer and an oncocytomas are difficult to distinguish and is only found after surgical resection.
Angiomyolipoma are common benign (noncancerous) tumours of the kidney composed of three types of cells: vascular cells, immature smooth muscle cells, and fat cells.

Angiomyolipoma’s are often found incidentally when the kidneys are imaged for other reasons, or as part of screening in patients with tuberous sclerosis. You may have presented with a palpable mass, flank pain, urinary tract infections, haematuria (blood in the urine), renal failure, or hypertension .
Although regarded as benign, they may grow such that kidney function is impaired or the blood vessels may dilate and burst, leading to bleeding.

Symptomatic presentation is most frequently with spontaneous retroperitoneal haemorrhage; the risk of bleeding is proportional to the size of the lesion (>4 cm diameter). Shock due to severe haemorrhage from rupture is described as Wunderlich syndrome (3)


Angiomyolipomas found incidentally usually require no therapy (when small), although follow-up is recommended to assess for growth. Small solitary AMLs (<20 mm) probably do not require follow-up due to their slow growth.
Larger AMLs, or those that have been symptomatic, can be electively embolised and/or resected with a partial nephrectomy. Lesions that present with retroperitoneal haemorrhage often require emergency embolisation as a life-saving measure. (3)


1. Renal Cell Carcinoma Guidelines (EAU, 2021)
Updated guidelines on the management of renal cell carcinoma (RCC) were published in October 2021 by the European Association of Urology (EAU) in European urology.

2. RSNA RadioGraphics Journal
Bosniak Classification of Cystic Renal Masses, Version 2019: A Pictorial Guide to Clinical Use
Nicola Schieda , Matthew S. Davenport, Satheesh Krishna, Elizabeth A. Edney, Ivan Pedrosa, Nicole Hindman, Ronaldo H. Baroni, Nicole E. Curci, Atul Shinagare, Stuart G. Silverman
Author Affiliations
Published Online:Apr 16 2021

3. Radiopaedia
Renal angiomyolipoma
Last revised by Dr Sonam Vadera◉ on 13 Apr 2022
Renal angiomyolipoma | Radiology Reference Article |
Author Affiliations
Published Online:Apr 16 2021