What is a frozen section, and do I need one?
In “An ordinary citizen’s ideal biopsy” I cover how a block of paraffin gets shaved to produce tissue slivers that end up on glass slides. A frozen section is obtained in the same way but, because a diagnosis is sought during the actual surgical operation, the method of solidifying the tissue is different. There is no time for overnight processing, since the surgeon needs a rapid opinion. Therefore, instead of being embedded in paraffin, the sample is placed into a thick gel that is immediately frozen solid in liquid nitrogen. The microtome for shaving the frozen block is housed in a cold chamber (the cryostat), where the cutting occurs (Fig. 4). As the cold sections peel away, they are affixed to slides and stained. The result is usually available within a few minutes, depending on the complexity of the case and whether other cases are being done concurrently.
Figure 4
In many hospitals, the frozen section laboratory resides within the operating suite, affording maximum interaction between pathologist and surgeon. However, the facility may be located in a different part of the hospital, in a different building on the campus, or even more distantly. The further from the operating room, the longer the tissue commutes before reaching the pathologist. Telepathology is now used in some remote locations to transfer microscopic images prepared by an on-site technologist to a pathologist who may be situated a hundred miles or more away. Ideally, however, the surgeon and pathologist should interact face-to-face. This is perhaps well illustrated by an example from my own experience.
I was handling a small specimen from a large abdominal mass. The surgeon walked in, asking for the diagnosis. We returned to the operating room, where I saw a heaving intra-abdominal mass, visible through a small opening. I suggested where he might take additional bites. He asked whether he had taken enough, so I went into my Oliver Twist routine and said no, I needed more. I wanted enough tissue to establish a definite diagnosis, as well as sufficient material for possible future tests. Next day, almost everything was uninterpretable, except for a morsel on only one out of six slides, and there the diagnosis was obvious. Had I not pressed for more, the pickings would have been altogether insufficient. Surgeons and pathologists can work in tandem to improve the likelihood of obtaining good results.
The primary purpose of the frozen section is to provide the surgeon with information that will influence the course of the operation. For example, if the surgeon wishes to know whether a tumor has been completely removed, tissue from the edge of the space formerly occupied by the lesion may be sent for a frozen section. Should the pathologist find residual tumor there, the surgeon may elect to excise more tissue. A frozen section performed purely out of curiosity, and without any anticipated effect on the conduct of the surgical procedure, not only wastes pathology resources but may also unintentionally compromise the ability of the pathologist to render an accurate final diagnosis. Freezing induces artifacts that distort cellular details, and one would not want this to happen on the most important (or only) material that emerges from the operation. The request for a frozen section activates a pathologist, a resident, a histotechnologist, and potentially others if things are extremely busy, and all of these individuals are then diverted from other diagnostic work. “Unnecessary” frozen sections delay action on patients whose surgeons really need intraoperative consultations, and elicit avoidable bills. Pathologists do recognize when it may be perfectly appropriate to perform a frozen section for psychological reasons, but as a standard approach, this does not constitute sound practice.
Pathologists are under great pressure when doing frozen sections, and may be involved in more than one case simultaneously. Resources, however, are usually not available for more than one at a time to be assigned to this duty. The College of American Pathologists recommends that an individual frozen section should take no more than 20 minutes, from receipt by the pathologist until an interpretation is called in to the operating room. In practice, when multiple requests for frozen sections arrive simultaneously, it is virtually impossible to meet this standard for each of them.