What are the indications for fine-needle aspiration cytology (FNAC)?

Indications for Fine-Needle Aspiration Cytology (FNAC)

FNAC is indicated for tissue diagnosis of palpable and non-palpable masses across multiple organ systems, but core needle biopsy is preferred when tissue architecture is required for definitive diagnosis, particularly in breast lesions and lymphomas.

Breast Lesions

Core needle biopsy is preferred over FNAC for breast masses, especially non-palpable lesions, due to superior diagnostic accuracy. 1

• FNAC may be used for palpable breast masses when performed by experienced cytopathologists, achieving high accuracy for cancer diagnosis 1
• Both core needle biopsy and excisional biopsy demonstrate greater accuracy than FNAC for evaluating non-palpable breast lesions 1
• FNAC requires pathologists with specific expertise in interpretation and necessitates follow-up tissue biopsy when atypia or malignancy is identified 1
• The minimally invasive nature and low cost are advantages, but these are outweighed by the need for confirmatory biopsies 1
• FNAC can provide same-day diagnosis in rapid assessment clinics with positive predictive value of 100% for definitive cancer diagnosis (C5), though sensitivity is 94% 2

Gastrointestinal and Pancreaticobiliary Lesions

EUS-guided FNAB is the preferred method for tissue acquisition from pancreatic masses, peri-intestinal lymph nodes, and adjacent organ pathology. 3

• Perform EUS-FNAB for mucosal and submucosal lesions where prior endoscopic biopsies were nondiagnostic 3
• Use for sampling peri-intestinal structures including lymph nodes, and masses in the pancreas, liver, adrenal glands, gallbladder, and bile duct 3
• Obtain tissue diagnosis before initiating neoadjuvant therapy for pancreatic cancer, where histologic confirmation is required 3
• For solid pancreatic tumors, EUS-FNAB achieves sensitivity of 90.8%, specificity of 96.5%, and accuracy of 91% 3
• Perform at least 6-7 passes on pancreatic masses when onsite cytopathology is unavailable to maximize diagnostic yield 1
• Diagnostic yield plateaus after 7-8 passes 1

Lymph Nodes and Lymphoma

Excisional lymph node biopsy is generally preferred over FNAC for initial lymphoma diagnosis, though FNAC has a role in specific circumstances. 1

• Core needle biopsy may be adequate for diagnosis, but excisional biopsy is recommended for Hodgkin lymphoma 1
• FNAC is insufficient as sole diagnostic assessment except when combined with immunohistochemistry and judged diagnostic by an expert hematopathologist or cytopathologist 1
• Lymphomas require flow cytometry for definitive subtyping; FNAC can suggest lymphoma but excisional or core biopsy provides superior sensitivity 4
• Perform at least 3 passes on lymph nodes when onsite cytopathology is unavailable 1
• Collect material in tissue culture media (Roswell Park Memorial Institute medium) for flow cytometry when lymphoid lesions are suspected 4

Head and Neck Masses

FNAC is indicated as first-line diagnostic approach for parotid gland masses and neck swellings, particularly when guided by ultrasound. 5, 6

• Use 21-25 gauge needles for standard FNAC of parotid masses, with 25-gauge offering better flexibility for superficial lesions 5
• Target the periphery rather than the center of masses, as centers are often necrotic and yield non-diagnostic tissue 5
• Employ a "fanning" technique by repositioning the needle at 4 different areas within the mass to increase diagnostic yield 5
• FNAC is suitable for assessment of neck swellings in outpatient clinics, with tuberculous lymphadenitis being the most common diagnosis (36%), followed by reactive lymphadenitis (18%) and malignant neoplasms (14%) 6
• Ultrasound-guided FNAC significantly improves diagnostic accuracy and specimen adequacy compared to palpation-guided techniques 4

Soft Tissue Masses

FNAC serves as an effective first-line or complementary diagnostic tool for soft tissue tumors, particularly for confirming metastatic disease or recurrence. 7, 8

• Use FNAC for initial pathologic diagnosis of primary benign and malignant soft tissue masses, with sensitivity of 100% and specificity of 97% in distinguishing benign from malignant lesions 8
• FNAC accurately subtypes 83% of malignant soft tissue tumors and 72% of benign lesions 8
• For primary soft tissue sarcomas, 63% can be accurately subtyped by FNAC 8
• FNAC is particularly valuable for pathologic confirmation of metastatic tumors to soft tissue and documentation of locally recurrent neoplasms 8
• The procedure is safe, simple, rapid, and has low morbidity with good sensitivity and specificity 7

Technical Optimization

The presence of an onsite cytopathologist or cytotechnician is the single most important factor for maximizing diagnostic yield. 1, 4

• Onsite cytopathology reduces inadequate samples from 12.6% to 1% and improves diagnostic sensitivity from 78.2% to 96.2% 4
• When onsite cytopathology is unavailable, perform adequate number of passes (3 for lymph nodes, 6-7 for solid masses) using fanning technique 1
• Prepare both air-dried smears (for Diff-Quik staining) and alcohol-fixed smears (for Papanicolaou staining) 1, 5
• Procure additional specimen for cell block preparation to enable immunohistochemistry, flow cytometry, and molecular testing 1, 4

Critical Limitations and Pitfalls

• FNAC has a significant learning curve, with diagnostic sensitivity improving from 30% in early cases to 80-90% after adequate experience 3
• False-negative results can occur; negative FNAC should not preclude additional diagnostic procedures when clinical suspicion remains high 4
• When initial FNA is indeterminate, repeat EUS-guided FNA yields correct diagnosis in 61-84% of patients with high clinical suspicion for malignancy 3
• FNAC is not acceptable as sole diagnostic tool when both morphology and immunophenotyping are required for classification 4
• Inadequate sampling occurs particularly in collagenous lesions and when performed by operators lacking experience 9