WHO 2022 Renal Cell Tumor Classification: Imaging Clues

A practical radiology review of WHO 2022 Renal Cell Tumor Classification: Imaging Clues, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

Why this topic matters

• WHO 2022 classification completely reorganized renal epithelial tumors.

Two new categories introduced

Other Renal Tumors

Molecularly Defined Renal Carcinomas

• Many tumors previously called pRCC type 2 have now been redistributed into these new categories.

Key message

Many rare tumors still show gradual enhancement like pRCC, but differ in

• Age
• Growth pattern
• Enhancement degree
• T2 signal
• Metastatic potential
• Radiologists should recognize these clues and suggest specific pathology/genetic testing.

Major WHO Categories

1. Clear Cell Renal Tumors

Clear Cell RCC (ccRCC)

• 65–70% of RCCs
• Imaging
• Expansile growth
• Pseudocapsule
• Marked heterogeneous enhancement
• Washout
• Intratumoral cysts (~30%)
• T2 hyper/isointense
• Opposed-phase signal drop (intracellular fat)

Remember

• Hypervascular solid renal mass without macroscopic fat = ccRCC until proven otherwise.

Differential

Oncocytoma

• Usually moderate enhancement
• No signal drop on opposed phase

Multilocular Cystic Renal Neoplasm of Low Malignant Potential

• 0.5–2.5%

Imaging

• Multicystic lesion
• No solid nodules
• Usually Bosniak IIF–III
• Indolent behavior

2. Papillary Renal Tumors

• Classic Papillary RCC
• 13–20%

Imaging Signature

• Hypovascular
• Gradual enhancement
• Homogeneous
• T2 hypointense
• Isoattenuating on noncontrast CT
• Pseudocapsule

Differential

Fat-poor AML

Fat-poor AML

• 45 HU on noncontrast CT
• T2 dark
• pRCC: Usually isoattenuating to cortex
• "T2 dark + gradual enhancement" = think pRCC first.
• Papillary Adenoma
• ≤15 mm
• Benign
• Common in elderly autopsies
• Usually monitored

3. Oncocytic & Chromophobe Tumors

Oncocytoma

• 3–7%
• Chromophobe RCC
• 5–7%

Imaging

• Expansile
• Pseudocapsule
• Homogeneous
• Moderate enhancement
• Washout
• T2 isointense
• Classic but unreliable signs
• Central scar
• Segmental enhancement inversion
• Can occur in both oncocytoma and ChRCC.
• Imaging differentiation remains difficult.

4. Collecting Duct Carcinoma

• <1%
• Highly aggressive
• Imaging
• Medullary origin
• Infiltrative growth
• Hypovascular
• T2 low/intermediate
• Renal sinus invasion
• Diffuse nephritis-like enlargement
• Frequent nodal/distant metastases
• Consider when kidney looks enlarged rather than mass-forming.

Important Rare Tumors

• Clear Cell Papillary Renal Cell Tumor (CCPRCT)
• 1–4%
• Indolent
• Imaging
• Often cystic
• Bosniak III–IV

Two patterns

• Hypervascular → resembles ccRCC
• Gradual enhancement → resembles pRCC
• Clues
• Younger patients
• Well defined
• Excellent prognosis

Mucinous Tubular and Spindle Cell Carcinoma (MTSCC)

• <1%
• Female predominance
• Good prognosis
• Imaging
• Gradual enhancement (like pRCC)
• T2 variable
• Isointense
• Hyperintense (mucin)
• Pseudocapsule
• Low ADC despite high T2
• Pearl pRCC-like enhancement + unexpectedly high T2 signal → think MTSCC.
• Tubulocystic RCC
• <1%
• Strong male predominance
• Imaging
• "Spongelike" appearance
• Clustered tiny cysts
• Bosniak II–III
• Hyperechoic on US
• Hyperechoic cystic lesion = clue.
• Acquired Cystic Disease–Associated RCC
• Long-term dialysis patients
• Imaging
• Gradual enhancement
• T2 dark
• Hemorrhage common
• Helpful MRI clue

Tumor

• Heterogeneous DWI hyperintensity

Hemorrhagic cyst

• Homogeneous DWI hyperintensity

Eosinophilic Solid & Cystic RCC (ESC-RCC)

• New WHO 2022 entity
• Female predominance
• Signature Finding
• "Lotus root appearance"
• Mixed macro- and microcysts throughout solid tumor
• Imaging
• T2 hypointense
• Moderate enhancement
• Washout or gradual enhancement
• Usually no pseudocapsule
• Lotus-root kidney tumor = ESC-RCC.

Molecularly Defined RCCs

• TFE3-Rearranged RCC
• Children & young adults
• Imaging
• Hyperattenuating (>45 HU)
• Calcifications common
• Gradual but stronger enhancement than pRCC
• T2 hypointense
• Restricted diffusion
• Often pseudocapsule
• Frequent nodal metastases
• Key Differentiator

pRCC-like but

• Younger patient, Calcified, Hyperdense on noncontrast CT, More heterogeneous
• → Think TFE3 RCC.

FH-Deficient RCC

• Aggressive
• Median age ~44 years
• Imaging
• Infiltrative growth
• Cystic components
• Gradual enhancement
• More enhancement than pRCC
• Heterogeneous T2
• T1 hyperintense hemorrhage
• Early nodal/distant metastases

Pearl: Young patient + infiltrative cystic renal mass + metastases = FH-deficient RCC until proven otherwise.

SMARCB1-Deficient Renal Medullary Carcinoma

• Very aggressive
• Classic Patient: Young patient Sickle cell trait
• Imaging
• Central medullary mass
• Infiltrative growth
• Hypovascular
• Necrosis
• Metastases common
• Restricted diffusion
• Sickle cell + infiltrative medullary tumor = renal medullary carcinoma.
• Take-Home Algorithm
• Hypervascular + washout ccRCC
• Hypovascular + gradual enhancement + T2 dark pRCC
• Moderate homogeneous enhancement Oncocytoma / ChRCC
• Infiltrative medullary mass Collecting duct carcinoma / Medullary carcinoma
• Young patient + calcified hyperdense pRCC-like mass TFE3 RCC
• Infiltrative cystic mass + metastases FH-deficient RCC
• Lotus-root appearance ESC-RCC
• pRCC-like enhancement + T2 brighter than expected MTSCC