What is the role of Endoscopic Ultrasonography (EUS) guided Fine Needle Aspiration Cytology (FNAC) in diagnosing intraabdominal lesions?

EUS-Guided FNAC in Diagnosing Intraabdominal Lesions

EUS-guided FNAC is the modality of choice for diagnosing indeterminate intraabdominal lesions, particularly subepithelial GI tract lesions, pancreatic masses, pancreatic cysts with high-risk features, and intra-abdominal lymphadenopathy, with diagnostic accuracies ranging from 75-100% depending on lesion characteristics. 1

Primary Indications for EUS-Guided FNAC

Subepithelial Lesions of the GI Tract

• EUS-guided FNA/FNB is indicated for indeterminate subepithelial lesions when forceps biopsies are non-diagnostic, serving as the definitive tissue acquisition method 1
• Diagnostic accuracy varies significantly by lesion size: 71% for lesions <2 cm, 86% for lesions 2-4 cm, and 95-100% for lesions >4-5 cm 1
• Fine-needle biopsy (FNB) needles demonstrate superior tissue acquisition compared to FNA needles (75-100% accuracy), with similar safety profiles 1
• 22-gauge and 25-gauge needles are more maneuverable and favorable for most positions, while 19-gauge needles are optimal for cyst aspirations 1

Pancreatic Cystic Lesions

• EUS-FNA is the preferred initial imaging modality when high-risk stigmata or worrisome features are present in pancreatic cysts 1
• For cysts ≥3 cm (a worrisome feature itself), EUS-FNA should be performed even without other concerning features, as this size confers a 3-fold increased malignancy risk 1
• EUS-FNA should be considered for any cyst ≥2.5 cm with at least one worrisome feature, as cysts ≥1.7 cm contain sufficient fluid for cytology and biomarker analysis 1
• The addition of EUS-FNA to diagnostic algorithms alters management in 72% of patients and reduces unnecessary surgeries by 91% 1

Key biochemical markers obtained via EUS-FNA:

• CEA <5 ng/mL suggests pseudocyst or serous cystadenoma 1
• CEA 192-200 ng/mL is 80% accurate for mucinous cyst diagnosis 1
• Amylase >250 IU/L suggests pseudocyst 1
• Cytological evaluation detects approximately 30% more cancers than imaging features alone 1

Pancreatic Solid Masses

• Repeat EUS-FNA after an initial non-diagnostic procedure yields correct diagnosis in 61-84% of cases when clinical suspicion for malignancy remains high 1
• Diagnostic accuracy reaches 92-95% for pancreatic masses, though a learning curve exists with sensitivity improving from 30% to 80-90% over the first 50 procedures 1

Intra-abdominal Lymphadenopathy

• EUS-FNA demonstrates 89.7% sensitivity, 98.3% specificity, and 93.5% overall accuracy for diagnosing lymphadenopathy of unknown etiology 2
• Lymph node morphologic features (roundness, echogenicity, homogeneity) on EUS do not reliably predict malignancy 2
• The median number of passes is 5 for adequate sampling 2

Diagnostic Performance Across All Intraabdominal Lesions

• Overall diagnostic yield of USG/EUS-guided FNAC ranges from 75.7-96.77% for intraabdominal masses 3, 4
• Sensitivity: 89.7-95.35%, Specificity: 98.3-100%, Accuracy: 93.5-96.43% 3, 5, 2
• Inadequate samples occur in only 3.2-10.3% of cases 3, 5

Diagnostic distribution in intraabdominal lesions:

• Malignant lesions: 52.6-70.3% 3, 5, 4
• Benign lesions: 24.4-37.2% 3, 5
• Non-neoplastic inflammatory lesions: 4.1% 4

Technical Considerations

Needle Selection

• FNB needles provide better tissue architecture preservation than FNA needles 1
• 19-gauge needles are most efficient for cyst aspirations but difficult to maneuver in the fundus and duodenum 1
• 22-gauge needles are optimal for small cysts (<2 cm) and difficult anatomic positions 1

Cell Block Preparation

• Cell blocks prepared from residual FNA material improve diagnostic precision in 15.55% of cases 3
• Cell blocks facilitate better morphologic assessment and more definitive cytopathologic diagnosis 3

Safety Profile and Complications

Cystic Lesions

• Prophylactic antibiotics must be administered and continued for up to 48 hours when aspirating cystic lesions to prevent infection 1
• Multiple needle passes and incomplete fluid aspiration increase infection risk 1
• Intracystic hemorrhage (change from anechoic to hyperechoic) requires immediate procedure termination and 2-hour hemodynamic monitoring, though clinically significant bleeding is rare 1

General Complications

• EUS-FNA has a low overall complication rate, with main risks including hemorrhage, perforation, infection, and acute pancreatitis 6
• The procedure is considered safe and well-tolerated across all intraabdominal locations 3, 5, 4

Factors NOT Affecting Diagnostic Yield

• Location of the lesion within the abdomen 4
• Sampling technique employed 4
• Number of needle passes (beyond a minimum threshold) 4
• Operator qualification level (attending vs. fellow) 4
• Lesion size (though accuracy does improve with larger lesions for subepithelial masses) 4

Clinical Algorithm

For subepithelial GI lesions: Perform EUS first for characterization; if indeterminate or concerning features present, proceed directly to EUS-guided FNA/FNB 1

For pancreatic cysts:

• Cysts <2.5 cm without worrisome features: MRI with MRCP preferred 1
• Cysts ≥2.5 cm with ≥1 worrisome feature: EUS-FNA 1
• Cysts ≥3 cm: EUS-FNA regardless of other features 1
• Any cyst with high-risk stigmata: EUS-FNA immediately 1

For solid pancreatic masses: EUS-FNA as primary diagnostic modality; if non-diagnostic and clinical suspicion remains high, repeat EUS-FNA rather than CT-guided biopsy to avoid needle tract seeding 1

For intra-abdominal lymphadenopathy: EUS-FNA when lymph nodes are accessible and etiology unknown, regardless of morphologic features on imaging 2