Advances in technology

Histology has made little progress in the last 200 years but is suddenly starting to catch up with other areas of pathology. In the 1960s and 70s, Electron Microscopy was the 'in' thing to do in pathology but that largely fell out of favour with the advent of immunohistochemistry which proved to be lots cheaper. Histology now finds itself closely linked with molecular biology thanks to immunohistochemistry and a technique, which demonstrates the presence of DNA and RNA fragments, called in-situ hybridisation (ISH - usually fluorescent ISH, therefore FISH).

Besides these techniques, others are developing such as tissue microarray technology which is our area of special interest. The tissue microarray (TMA) technology was born in 1998 when Kononen et al. created the first TMA blocks using a precision instrument which had been specially constructed for the purpose (see Beecher Instruments). Briefly described, the method allowed for up to 1000 tissue samples to embedded, at known co-ordinates, in a single paraffin-wax histology block. This allows for large savings in tissue samples, reagents, time & money. While the majority of workers are using instruments, such as that produced by Beecher, to construct their array blocks, it is possible to make TMA blocks by transferring tissue samples manually from donor blocks to the recipient block.

On the right, you can see the type of needles used to make TMA blocks. The needles are used to make holes in the recipient blocks and also to extract material from routinely processed histology blocks. Finally, these same needles are used to insert sampled tissue fragments into the recipient block. What you can't see in this picture is that these needles, and the stylets that run through them, are less 2cm in length and only 0.6mm in cross section. These examples were manufactured by Beecher Instruments.
H&E stained slides from conventionally prepared blocks are generally reviewed by a pathologist as a guide; areas of interest are marked on the slide which can then be overlayed on the block to show technical staff where to insert the sampling needle. The needle's contents can then be pushed out, by means of the stylet, into the waiting holes in a recipient block. As mentioned above, there may be up to 1000 useful spaces in the recipient block but this is only possible if a machine has been used. If the blocks are prepared manually, the reduced accuracy means that only a few hundred samples can be included, as shown in this picture. (Sorry about the reflection.) Each little brown dot is a sample of tissue, 0.6mm in diametre, inserted upright into the face of the block (that is, perpendicular to the plane of sectioning).
Once all the samples are in the recipient block, it is warmed to allow the wax of the block to merge with that in the tissue samples. After that, it can be sectioned by conventional microtomy, resulting in slides with hundreds of dots of tissue on them. While these dots are very small (0.6mm diam.) there is usually sufficient material visible under the microscope to be able to grade the results of H&E, immunohistochemistry or FISH staining. In these pictures, you can see 1) An overview of the slides, showing their 'dotty' appearance 2) An H&E stained 'dot' under the microscope and 3) A 'dot' stained by the immunohistochemistry method, for the CAM 5.2 low molecular weight cytokeratins.	(1)
	(2)
	(3)