1-12 Kidney FNA: R Tambouret MD, E Brachtel MD, R Arpin CT
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Indications for Kidney Fine Needle Aspiration Cytology/Biopsy
Procedure — Biopsy is usually performed as an outpatient procedure under CT or US guidance with conscious sedation. At MGH a coaxial approach is used which entails per cutaneous insertion of a sheath with stylet (e.g. 10 cm coaxial 17 gauge Temno needle) into the lesion. The stylet is then removed and smaller needles are inserted to obtain fine needle Aspiration cytology and 18 gauge core biopsies. Percutaneous biopsy is safe with a very low risk of clinically significant bleeding or seeding of the needle tract with malignant cells. Rapid on site evaluation (ROSE) by the cytology team is rarely requested at MGH unless a concurrent ablation is planned. Usually though the ablation is done as a second procedure after the FNA. Exceptionally the FNA may be performed by a gastroenterologist with endoscopic ultrasound guidance. The test demonstrates sensitivity and specificity of 80 to 92 percent and 83 to 100 percent, respectively, for the detection of cancer and is especially helpful in differentiating RCC from a metastasis. At MGH, the radiologist will make alcohol fixed smears and will also rinse the needle in an appropriate alcohol solution (e.g. CytoRichRed for SurePath processing). In other practices may also pathologists may request air-dried smears for Giemsa staining in addition to alcohol fixed slides. The core biopsy is fixed immediately in 10% formalin.
At MGH, the radiologist will make alcohol fixed smears and will also rinse the needle in an appropriate alcohol solution (e.g. CytoRichRed for SurePath processing). In other practices may also pathologists may request air-dried smears for Giemsa staining in addition to alcohol fixed slides. The core biopsy is fixed immediately in 10% formalin
The cytology report includes a statement of adequacy (adequate, evaluation limited by ...., unsatisfactory), the interpretation category (No malignant cells, Atypical, Suspicious for malignancy, Positive for malignant cells) and the Diagnosis (there are some drop down menu choices or the pathologist can free text the diagnosis). The core biopsy diagnosis is included under the cytology N number as part B. Currently Two H&E ribbons are produced for the core biopsy.
Basic Cytomorphology
- Proximal Convoluted Tubule (PCT): tubules and sheets, abundant granular cytoplasm, ill-defined fragile cytoplasm without cell borders (unlike oncocytoma)
- Bland nucleus, prominent nucleolus, mimics: oncocytoma, RCC
- Distal Convoluted Tubule/collecting Duct (DCT/CD): tubules, flat sheets (unlike RCC)
- Well-defined cytoplasm
- Smaller cells, no vacuoles (unlike RCC)
- No nucleolus, mimic: RCC
- Capillary loops best seen on the periphery of the cell group
- Very cellular, spindled and round cells in a crowded structure, the glomeruli may retain their round shape or may be drawn out into an irregular or ovoid shape during smearing
- No atypia
- No spherules or papillae (unlike papillary RCC)
- Beware of a smear containing both glomeruli and tubules, the radiologist may have missed the lesion or the abnormality seen on imaging may * be non-neoplastic
- Clear Cell Type (CRCC): clean or necrotic background
- Cohesive monolayered sheets or crowded groups with a mixture of cells with granular cytoplasm and cells with clear or finely vacuolated cytoplasm (clear cells may be in the minority) (unlike oncocytoma)
- Prominent branching capillaries traverse the crowded cell groups
- Usually round nuclei, variable nucleoli
- Impox: Vimentin, cytokeratin, CD10, RCC, PAX8, PAX2 positive
- Hale's colloidal iron negative
- MIMICS: glomeruli, distal convoluted tubule and collecting duct, oncocytoma, chromophobe RCC
- Chromophobe Type: sheets, clusters, single cells with granular cytoplasm
- Bare nuclei (unlike oncocytoma)
- More variation in cell & nuclear size than oncocytoma
- Vesicular round nuclei, binucleation, inclusions, irregular nuclear outline prominent nucleoli in some
- Abundant granular cytoplasm, perinuclear clearing, prominent cell borders ("koilocytic"), fluffy/clear/granular not uniform cytoplasm,
- Impox and special stains: vimentin negative, cytokeratin 7 positive , CD 10 and RCC equivocalHale's colloidal iron positive - uniform, dense, cytoplasmic, (tricky stain, often deceptively pale and uneven in chromophobe) ,: differential diagnosis: oncocytoma, CRCC
- Papillary RCC: small unform cells with scant basophilic cytoplasm (type 1) or more abundant eosinophilic cytoplasm (type 2) in three dimensional spheres or in papillae with cores containing foamy histiocytes; tumor cells and histiocytes may contain hemosiderin
- Impox: AMACR, CD10, RCC positive; CK7 positive more often in type 1 than type 2
- Dyshesive single cells or loose clusters
- round nuclei, smooth borders (but occasional nuclear atypia)
- Binucleation, inconspicuous nucleoli
- Abundant uniformly granular well-defined cytoplasm, no vacuoles
- Vimentin Negative, Cytokeratin 8/18 Positive
- Hale's Colloidal Iron Negative, or Perinuclear/atypical Staining Present, MIMICS: PCT, Chromophobe RCC, Conventional RCC with Granular Cytoplasm
