1. Field of the Invention
This invention relates to tissue cassettes and, more particularly, to a tissue cassette suitable for holding a biological tissue specimen while it is being treated with fluids for holding embedding tissue in a microtome for microscopic examination.
2. Description of the Prior Art
Processes for examining thin tissue slices under the microscope are well-known in the art. The tissue specimens are gathered generally through biopsies taken during exploratory surgery. They are then positioned within tissue cassettes. The tissue cassettes are then placed in a histological tissue processing chamber such as disclosed in U.S. Pat. No. 4,141,312. The chamber heats the tissue and treats the tissue with various chemicals, such as alcohols, xylene and formaldehydes. This preserves the tissue which is then embedded in paraffin in the tissue cassette. The embedded blocks are then sliced on a microtome and subsequently stained and observed by a pathologist under a microscope.
Cassettes for holding the tissue specimens are well-known in the art, for example, see U.S. Pat. Nos. 4,220,252 and 4,421,246. Both of these patents disclose tissue cassettes molded from a plastic material. Earlier tissue cassettes were manufactured with stainless steel and were expensive to make. The newer plastic tissue cassettes are much less expensive to make. Generally, patient information, such as a patient number, is directly placed on the tissue cassette for identification of the processed tissue.
Typically, the plastic tissue cassettes have a lid and an open top base member. The lid connects to the base member by an integral hinge or gate. The plastic hinges must be very thin, on the order of several thousandths of an inch, for flexibility. Hence, the hinges are frangible and usually break upon either connecting the lid to the base member or upon disconnecting the lid from the base member. This is due to both the physical properties of the plastics used, which must withstand the effects of the chemicals used in preserving the tissue, and the hinge thickness. Only a limited number of plastics can be used in the tissue processing environment. Therefore, the hinges on the plastic tissue cassettes usually do little more than keep the lids attached to the top base member prior to use.
Should a histologist want to examine a tissue specimen during the preserving processes, he or she must open the tissue cassette. Usually, by this time, the hinge is broken and the tissue cassette is in two pieces. If the tissue needs more processing, then the two pieces are connected to each other and the tissue cassette is replaced into the chamber for further processing. There is a possibility that the two-part tissue cassette will open up during this second processing, causing the tissue to fall into the chamber. Further, even if the hinge does not break immediately, the tissue cassette could open up during processing.
In practice, usually over one hundred tissue cassettes with specimens are processed at a time. These specimens come from a variety of patients who have very recently had exploratory surgery. If more than one tissue cassette opens during processing and the tissues fall into the chamber, more exploratory surgery may have to be done on the patient.
Therefore, it is an object of my invention to provide a plastic tissue cassette having a lid connected to the base member by a hinge which does not break in normal operation.
It is another object of my invention to provide a tissue cassette that remains closed during the tissue processing stage.
With various diseases, such as AIDS, lab technicians are ever wary about handling samples from patients having these diseases. Typical lab procedures for technicians processing tissues of patients having AIDS include wearing several layers of latex gloves while handling the tissue cassettes. This limits the possibility of the AIDS virus from entering the technicians, bodies through an open wound on their hands.
As mentioned above, the prior art plastic tissue cassette hinges usually break when the tissue cassette is first closed or first reopened. Typically, the broken hinges are jagged enough to cut through the technicians, two pairs of latex gloves and the technicians, hand. In fact, a common injury to the technicians prior to the above added precautions were cuts to hands from jagged edges of the broken hinges.
Therefore, it is a further object of my invention to provide a tissue cassette which decreases the possibility of a technician being injured by a broken hinge of a plastic tissue cassette.