Sampling the gastrointestinal tract
Cytologic evaluation of GIT lesions is often performed in animals to aid diagnosis of solid masses or infiltrative GI disease. Even with concerns for devitalized tissue, complications from sampling are rare but can include bleeding, infection, and acute pancreatitis (Karadsheh & Al-Haddad, 2014).
Several factors can influence the diagnostic yield of a sample including presence of necrosis, secondary inflammation, hemodilution, cell rupture, or poor exfoliation (Rivers et al., 1997; Bonfanti et al., 2006; von Babo et al., 2012). Certain lesions affecting the GIT, such as chronic enteropathy, low-grade lymphoma, and poorly differentiated tumors, can be difficult to diagnose by cytology alone, and histology is typically needed for architecture and special staining. However, many GI lesions can be preliminarily or even definitively diagnosed by cytology of fine needle aspirates (FNAs), impression smears, or exfoliative cytology and rectal scrapes (Jergens et al., 1998; Dell’Orco et al., 2005; Bonfanti et al., 2006; Maeda et al., 2017).Impression smears
Touch imprints from tissue samples acquired by endoscopic or full-thickness biopsies are excellent for the diagnosis of GI lesions. Touch imprints are often performed for quick interpretation of a lesion in order to begin initial treatment prior to obtaining final histopathology results. Care must be taken to avoid crushing the tissue or applying too much pressure while making impression smears, as cell rupture may confound the diagnosis.
Fine needle aspiration
Many reports have recognized the benefit of the co-utilization of imaging modalities such as endoscopy and ultrasound-guided FNA. Effective techniques to improve cell yield and minimize cell destruction have been proposed for cytologic samples. For obtaining diagnostic samples via FNA, factors such as needle size, aspiration/suction versus nonaspiration techniques, and lesion location have all been evaluated (Karadsheh & Al-Haddad, 2014). With regard to needle size, most studies show no difference between the use of 22-gauge versus 25-gauge needles.
Aspiration may be superior for obtaining cells, particularly from fibrotic lesions or mesenchymal tumors. However, aspiration may result in increased hemorrhage or, in the case of lymphoproliferative lesions, increased cell rupture (Karadsheh & Al-Haddad, 2014).Exfoliative cytology
In addition to FNA or impression smears post-biopsy of lesions in the GIT, exfoliative techniques such as brush cytology and rectal scrapings may be employed. (Rectal scraping is discussed further under ‘Large Intestine [Cecum, Colon, and Rectum’].) In brush cytology, samples are acquired via endoscopy using a disposable guarded cytology brush instrument, which is passed through the accessory channel of the endoscope. The brush is extended beyond the protective sheath and rubbed or twirled vigorously over the mucosa to dislodge cells, then retracted back into its sheath and withdrawn. After removal, the brush is rolled across a slide to transfer the material for subsequent staining (Jergens et al., 1998).
Regardless of the technique utilized to obtain a sample, care should be taken to avoid excessive pressure during transfer and spreading of material onto a slide, as excessive pressure often results in cell rupture (Jergens et al., 1998). Preparations made by FNA, impression smears, and brush exfoliation from endoscopic tissue biopsy have all been compared with histologic diagnosis for GI lesions (Rivers et al., 1997; Jergens et al., 1998; Bonfanti et al., 2006; von Babo et al., 2012; Karadsheh Al-Haddad, 2014). In most reports, despite the pitfalls mentioned above, good accordance has been shown, particularly for impression smears of tissue samples (Bonfanti et al., 2006; von Babo et al., 2012); therefore cytology remains a good technique to evaluate lesions, particularly neoplasms, in the GIT.