Papillary renal cell carcinomas (pRCC) are the second most common histological subtype of renal cell carcinoma (RCC).

Epidemiology

This subtype may account 13-20% of all renal cell cancer ¹. This subtype is also the most common in the renal transplant population ¹¹. There is slightly increased male predilection. 

Associations

• hereditary leiomyomatosis and renal cell carcinoma
• hereditary papillary renal cell cancer type 1

Clinical presentation

As with other types of renal cell cancer, most are asymptomatic and incidentally discovered.

Pathology

There are two subtypes described according to morphology ⁷:

• type I
  • have papillae covered by a single layer of cuboidal or low columnar cells with scanty cytoplasm and low-grade nuclei
  • carry a better prognosis than type II tumours
• type II:
  • are of a higher nuclear grade and contain more than one layer of cells with abundant eosinophilic cytoplasm
  • although mostly unilateral, this subtype is considered the most common to result in bilateral renal cell cancers ¹

While it has been described to have a tendency to present at a lower stage, it still has a distinct potential for progression and aggressive behaviour ⁴.

Radiographic features

Although there is no absolute rule, in general, papillary renal cancers at diagnosis tend to have a smaller mean diameter and be at a lower stage. The imaging features of type 1 and type 2 tumours may overlap.

Ultrasound

Generally tends to be hypoechoic on ultrasound ⁹.

CT

Smaller lesions tend to be homogeneous in attenuation with larger tumours tending to be heterogeneous.

These tumours are characteristically less vascularised than the more common clear cell subtype, showing overall hypoenhancement compared to the adjacent normal renal cortex, particularly seen in the corticomedullary phase.

When not enhancing at all, it can be difficult to differentiate from hyper-attenuating cysts ⁸. 

MRI

The tumours generally present with a pseudo-capsule. 

• T1: hypointense
• T2: hypointense
• T1 C+ (Gd): contrast enhancement tends to be less intense than in the more common clear cell RCC subtype
• DWI: restricted diffusion may be useful for differentiating from a haemorrhagic cyst

See also

• WHO classification of tumours of the kidney