Vet360 Vet360 Vol 05 Issue 04 - Page 6

CPD ACCREDITED ARTICLE B) Tru cut biopsies • Advantage: permits some evaluation of architecture, are minimally invasive and multiple samples can be obtained. • Disadvantage: a small amount of tissue is collected, and so only limited architecture can be evaluated, which may lead to an incorrect interpretation. Like looking through a porthole. C) Punch biopsies. • These biopsies were designed specifically for skin biopsies in dermatology pathology (and should not be used for other system purpose). D) Endoscopic and laparoscopic biopsies. • Advantage: it is a minimally invasive procedure to observe and sample tissues and organs otherwise not available without open laparotomy, thoracotomy or cystotomy. Corrective or therapeutic surgery can be performed at the same time. • Disadvantage: small tissue sample size, although larger than the other needle biopsy techniques. Only muccousal biopsies taken, the muscular layers are inaccessible. General anaesthesia is required drives up the costs. There are a unique set of issues related to specimen orientation and induced artefacts, as a consequence of the small size and friable nature of the samples. E) Incisional biopsies. • Advantage: provides a far greater amount of tissue in the other techniques. No special tools are required beyond scalpel and forceps. Cytology can be performed on the same specimen. As the sample is larger there is less likelihood of handling artefacts which distort the tissue. • Indications: performed when an excisional biopsy cannot be obtained. F) Excisional biopsies. • Advantage: 100% of the lesion can pre-provided for examination. Diagnosis and treatment can be incorporated in the same procedure. • Contraindications: when the lesion is too large or in an inoperable location. Representative of the pathological process Pathologists frequently make the fundamental error of assuming that the biopsy they receive contains the lesion. Neoplastic processes differ remarkably in their vet360 Issue 04 | SEPTEMBER 2018 | 6 distribution through tissues and organs. Therefore, biopsies that do not provide the entire lesion often do not produce tissue sections that are representative of the neoplastic process. In uniform lesions the neoplastic process is diffused and involves similar cells, such that sampling at any site yields the same diagnostic tissue, as might be observed with hepatoid adenoma or hepatoma etc. Non-uniform lesions are punctuated or even dominated by non-specific secondary or reactive changes which obscure diagnostic lesions. Osteosarcoma, mammary gland neoplasia, splenic haemangiosarcoma, soft tissue sarcomas etc. frequently induce necrosis, inflammation or stromal reaction scattered throughout the lesion and in very small biopsies may not be accompanied by the underlying neoplastic condition. The lesion may not be present or included in the biopsy because either it was not sampled or due to the complication of necrosis, inflammation and reactive tissue. Always use techniques that permit direct visualization of the tissue being sampled (ultrasound- guided, CT guided etc.), take multiple tissue samples, take the interface with normal as well as areas that look different. Sufficiently free of artifacts Artefacts are structures or substances not normally present but produced by some external agent. Artefacts which prevent interpretation are termed fatal. The most common artefacts encountered are related to the collection and handling of specimens both during and immediately following the biopsy procedure. • Surgical crush artefact. • Cautery artefact or thermal injury. • Freezing artefact. Fixation Fixation is the singularly most important step in producing good histopathology slides. 1. No tissue placed in formalin should ever be thicker than 0.5-1.0 cm in thickness. 2. The amount of formalin should be at least 10 – 15 times the volume of tissue placed in it. Large specimens such as spleens and large masses should be bread sliced into 1 cm slices to ensure adequate penetration of the formalin fixation. Large pieces of tissue contain sufficient extracellular fluid that they can dilute the formalin to substantially less than 10%, resulting in the tissue in the jar undergoing autolysis. Autolysis not only interferes with diagnosis, but impairs accurate mitotic index counts and frequently compromises tumour marker immunohistochemistry.