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renal masses and cysts

introduction

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⁾

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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

renal angiomyolipoma (AML)
- the most common benign (noncancerous) tumor of the kidney, primarily composed of blood vessels, smooth muscle, and fat.
- while small tumors are harmless and often found incidentally, they carry a risk of spontaneous, life-threatening bleeding if they grow larger than 4 cm resulting in:
  - sudden, sharp flank or back pain
  - haematuria
  - anaemia
  - high blood pressure
- an “epithelioid” variant contains little to no fat and can sometimes be misdiagnosed as kidney cancer.
- 80% of AMLs are sporadic
- 20% are associated with tuberous sclerosis in which case they tend to be at a younger age, are more numerous, grow faster, and occur in both kidneys
- Rx if larger than 4cm:
  - embolization
  - everolimus (Afinitor) is an mTOR inhibitor that can shrink angiomyolipomas, particularly those associated with tuberous sclerosis
  - surgery:
    - if the tumor is massive, has ruptured, or is difficult to differentiate from cancer
    - partial or complete kidney removal (nephrectomy) may be required

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