renal masses and cysts

see also:

• polycystic kidney disease
• renal malignancies
• renal medicine (nephrology)
• renal abscesses and perinephric abscesses

• it is common to have an incidental finding of cysts on kidneys on a CT KUB or CT abdo scan
• some should have a renal USS to further elucidate their nature and determine whether the patient should be referred to urology or renal medicine (nephrology)
• the Bosniak classification system has been created to help address this:
  • Bosniak I or II ⇒ ignore
  • Bosniak IIF ⇒ follow up - perhaps in 6 months
  • Bosniak III or IV ⇒ excise
• the following imaging features indicate that a cyst is NOT simple:
  • calcification
  • hyperdense / high signal
  • septations
  • multiple locules
  • enhancement
  • nodularity / wall thickening
• indications for excision are thus one or more of the following:
  • calcification status: enhancement, nodular and wall thickening
  • hyperdens status: poorly defined heterogeneous enhancement; solid on USS;
  • septations status: thick, irregular, nodular enhancement
  • enhancement level: > 15 Hounsfield Units increase of the mass after contrast injection (indicates vascularity)
  • multiloculated (unless due to infection)
  • all nodules other than very small non-enhancing nodules
  • wall thickening (unless due to infection)¹⁾

.

• simple cyst, imperceptible wall, rounded
• work up : nil
• % malignant : ~ 0%

• minimally complex
• a few thin (< 1mm) septa
• may contain fine calcifications or a small segment of mildly thickened calcification.
• non-enhancing high-attenuation (due to to proteinaceous or haemorrhagic fluid) renal lesions of less than 3 cm are also included in this category
• these lesions are generally well marginated.
• work up : nil
• % malignant : ~ 0%

• minimally complex but requiring follow up.
• increased number of septa, minimally thickened or enhancing septa or wall
• thick or nodular calcium may be present
• hyperdense cyst that is:
  • > 3 cm diameter
  • mostly intrarenal (less than 25% of wall visible);
  • no enhancement
• work up : needs ultrasound / CT follow up
• % malignant : ~ 25 %

• indeterminate, thick or multiple septations, mural nodule, hyperdense on CT (see 2F)
• treatment / work up : partial nephrectomy or RF ablation in elderly / poor surgical risk
• % malignant : ~ 54%

• clearly malignant, solid mass with large cystic or necrotic component
• all the characteristics of category III lesions but also with enhancing soft tissue components independent of but adjacent to the septa
• treatment: partial / total nephrectomy
• % malignant : ~100%

• 33% of people older than 50 years develop renal cysts but most are simple cysts
• multicystic dysplastic kidney (MCDK) - developmental
• genetic:
  • juvenile nephronophthisis (JNPHP)
  • polycystic kidney disease
  • medullary cystic kidney disease (MCKD)
  • glomerulocystic kidney disease (GCKD)
  • Von Hippel-Lindau syndrome (VHLS) - CNS hemangioblastoma (Lindau tumor), bilateral and multicentric retinal angiomas, renal cell carcinomas, pheochromocytomas, islet cell tumors of the pancreas.
  • tuberous sclerosis (TS)
• acquired:
  • simple cysts
  • acquired cystic renal disease - bilateral
  • medullary sponge kidney (MSK) - usually benign, asymptomatic, congenital disorder often detected in 20-40yr olds, but may cause UTI, renal stones, haematuria and distal renal tubular acidosis type 1. Causes tubular ectasia and dilated collecting ducts rather than large cysts.
  • renal angiomyolipomas
• malignant:
  • cystic renal cell carcinoma (RCC)
  • renal malignancies