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Fine needle aspiration (FNA) and other sampling methods

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Fine needle aspiration (FNA)

Fine needle aspiration (FNA) is the sampling method of choice for evaluating pancreatic masses. It is a procedure with few complications which can confirm malignancy in a minimally invasive manner. It is effective in the diagnosis of tumors, but cystic pancreatic lesions and non-neoplastic processes may also be evaluated by FNA.

Transabdominal ultrasonography or computed tomography can be used in the guidance of percutaneous pancreatic FNA. Needles of varying caliber, tip design, length and shape are available. Fine needles are divided into small (20-22 G), intermediate (19 G) and large (18 G).

Needle placement techniques vary depending on the imaging technique, the selected path of needle sampling and the location of the lesion. The tandem technique involves placing a guiding needle to serve as a reference point for the second, biopsy needle, and is most useful in CT-guided FNA where real-time visualization of needle insertion is impossible. The coaxial technique involves inserting a larger caliber needle to localize the lesion; a smaller caliber needle is the inserted through the larger one to sample the lesion. This method permits multiple sampling attempts.

Most recently, endoscopic ultrasound has emerged as a method of guidance for pancreatic FNA. It permits real time visualization of the needle tip, a better visualization of small lesions and identification of local metastasis or invasion of local structures.

Indications of pancreatic FNA cytology

The main indication for cytologic sampling of the pancreas is a radiologically detected mass suspected for malignancy. Radiologic evaluation provides information about the location, extent and nature of the lesion.

FNA of resectable lesions:

  • Medical-legal issues related to a bad outcome with benign disease: 10% of jaundiced patients
  • with an ‘obvious’ malignant mass prove to have a benign lesion
  • Potential for lymphoma diagnosis, a non-surgical disease
  • Cystic lesions
  • Patient compliance

FNA of non-resectable lesions:

  • Not all  large masses that appear unresectable are ductal adenocarcinoma
  • Advances in surgical and anaesthetic practices have improved surgical outcomes even in older,
  • less fit patients
  • A positive tissue diagnosis is mandatory before chemotherapy or radiation therapy can be instituted

Sensitivity and specificity

The sensitivity and specifity of FNA for pancreatic malignancies are high when they are performed by an expert operator. The presence of a pathologist improves sampling and sensitivity by ensuring adequate tissue collection and sample preparation.

The most common causes of false-negative diagnoses are sampling error and failure to recognize a well-differentiated adenocarcinoma. False-positive diagnoses are far less common and typically result from over-interpretation of reactive atypia in the setting of pancreatitis.

Controindications and complications

There are few controindications to pancreatic FNA, including bleeding disorders and lack of a safe access route.
Minor complications include vasovagal reaction. The most common major complication is acute pancreatitis; other rare major complications are pancreatic duct leaks, massive hemorrage and septic shock.

Slide preparation

Direct smears are made at the time of needle aspiration or duct brushing in the radiology suite. Half of the slides are air-dried and Diff-quick stained for immediate evaluation and assessment of specimen adequacy. The other half are alcohol-fixed and Papanicolaou stained. The residual material in the needle or on the brush is rinsed in a normal saline-based solution and can be used to prepare cytocentrifuge slides or cell blocks. Alternatively, the brushing or aspirate material may be deposited entirely in an alcohol-based solution for preparation of thinlayer slides or cell blocks.

It may be necessary to perform a dedicated needle pass for the collection of the material for ancillary studies such as immunocytochemistry, flow cytometry or cytogenetics. Aspiration of cystic lesions may involve collection of the fluid for analysis of tumor markers, pancreatic enzymes and viscosity.

Other sampling methods

Suspected pancreatic malignancy can also be sampled by pancreatic duct or common bile duct brushings, particularly when there is a ductal stricture without an obvious pancreatic mass. Brushings can be performed during endoscopic retrograde cholangiopancreatography or percutaneous transhepatic cholangiography. This method is more sensitive for diagnosing biliary tract cancer, but it is also effective for pancreatic malignancies involving the head of the pancreas (see biliary tract cytology).

Procedures for endoscopic ultrasound-guided fine needle aspiration

In the diagnostic armamentarium against pancreatic cancer, EUS has been shown to be extremely accurate in detecting pancreatic masses, which other imaging modalities sometimes fail to show. It is very sensitive in the local staging of the disease – especially when there is need to assess the size of the tumour and its relationship with the adjacent structures, and, even more importantly, it enables cytological confirmation through FNA at a single procedure. In an ideal world each EUS procedure would benefit from the presence of a cytopathologist assessing the adequacy of material, suggesting processing pathways and even diagnostic differentials, but in practice it is more cost-effective and just as efficient to train biomedical scientists (BMS) for this. Rapid assessment can also be consistently performed with telecytology.  Moreover in the provision of a centralised cytology service the use of liquid-based cytology (LBC) allows for optimal preservation of the samples which can withstand not always efficient transportation arrangements.  In our practice a senior BMS attends the clinic and assesses the material on a rapid stain (Diff-Quik®): air-dried and ethanol-fixed smears of each pass are prepared. A dedicated pass is also used entirely for LBC (ThinPrep®). As in all other areas of cytology experienced clinicians can provide high quality smears,but lack of experience or low volume of cases are the most important contributing  factor associated with a high number of inadequate or non-contributory samples, especially in cystic lesions.

Different types of cytological samples are available for pancreatobiliary cytology, the most common being biliary brushings/aspirates and EUS-FNA cytology from solid and cystic lesions of the pancreas. While all exfoliative cytology (brushings/aspirates and cyst fluids) are processed as LBC vials, FNA samples are both air-dried for rapid stains and intra-procedural assessment of adequacy as well as alcohol-fixed for Papanicoloau staining; in addition a whole pass is also included in a LBC vial for immunocytochemistry or molecular studies. A cell block is prepared directly from the vial when cellularity is sufficient. 28 In the case of cysts the fluid is separately submitted for carcinoembryonic antigen (CEA), amylase, CA125 and CA19.9 testing.