The CHTN also offers investigators macrodissected tissue to create tissue samples enriched for a particular cell type. Macrodissection refers to gross manual dissection of a frozen tissue sample embedded in OCT or a fixed tissue sample embedded in paraffin guided by a histologic section. A diagnostic pathologist analyzes the histologic section in order to identify areas of the specimen containing the tissue of interest and marks the guide slide appropriately. The marked guide slide is used by the technician to isolate those portions of the sample.
Two different methods of macrodissection are employed, block trimming method or target tissue dissection method. The choice of method depends on the characteristics of the particular target tissue and the particular tissue sample to yield the greatest yield and enrichment of target cells, and on the requirements or preferences of the investigator to be served.
The block trimming method is best used when the target tissue makes up a fairly large and uniform proportion of the tissue specimen, up to approximately 1 cm diameter. The target tissue dissection method is best used when the target tissue makes up small discrete areas (only a few mm in diameter) in the tissue sample.
A pathologist examines a histologic section of the embedded tissue microscopically and circles on the section with an indelible marker the area(s) of target tissue that meets the requirement of the study. Using the circled histologic sections as a guide, the target areas are then dissected from the tissue using a pointed scalpel blade, generally incising into the tissue for a depth of approximately 2 mm. The dissected area is then collected into an appropriately sized sealable tube.
Though better defined than a non-dissected tissue sample, the actual percentage of targeted cells obtained by macrodissection can only be proscribed to the degree that tissue architecture and admixed cellular components allow. This will vary from tissue type to tissue type and from case to case. Although the percentage of target tissue can be estimated with a greater degree of precision than with a non-dissected tissue sample, this is still an estimate and not an absolute quantification of captured tissue.
