Patent Publication Number: US-2007116612-A1

Title: Prefix tissue cassette

Description:
This claims the benefit of pending provisional application Ser. No. 60/732,549, filed on Nov. 2, 2005 (pending), the disclosure of which is hereby fully incorporated by reference herein. 
    
    
     TECHNICAL FIELD  
      The present invention relates to devices for the transport of tissue from a harvesting site to a pathology lab, more particularly, but not exclusively, to a tissue cassette for transporting tissue from a harvesting site to a pathology lab.  
     BACKGROUND  
      Screening tissue samples for disease is an extremely common practice in modern medicine. Otherwise known as a biopsy, a patient has tissue samples harvested from their body by a physician or other medical professional and then transported to a pathology lab in a container filled with tissue preservative for slide preparation, review, and diagnosis. When tissue is deposited unrestrained into tissue preservative solution it can curl and contort as it hardens. Some examples of tissue types that are prone to curl are colon tissue and skin tissue, however, other types of tissue curl or distort as well.  
      More specifically, after the physician or other medical professional has harvested the tissue and obtained the biopsy sample, the biopsy sample is then placed into what is known as a “fixing solution” preservative solution. The fixing or preservative solution is commonly a solution of buffered formaldehyde known as formalin. For example, a biopsy sample is commonly harvested by using a sharp, hollow needle to gather tissue inside the lumen of the needle. Accordingly, the biopsy samples are commonly long and skinny and rather snake-like. The preservative solution will kill the pathogens to protect the safety of the pathology lab workers. The tissue can curl up into a ball or take on other three dimensional contortions. Therefore, by the time the biopsy samples have arrived at the pathology lab, they may have hardened or semi-hardened into contorted shapes.  
      The tissue samples must be embedded in a paraffin block for sectioning and subsequent diagnosis. The biopsy samples must be reconfigured to be perfectly flat in the paraffin mold. Any contorted or curled biopsy sample must be straightened before embedding in the paraffin. Without straightening the tissue sample, a misdiagnosis could occur for reasons to be discussed below. Straightening these biopsy samples is difficult because a high level of precision is necessary and the size of the sample is often extremely small.  
      After the sample has been embedded, a microtome is used to slice very thin sections of the biopsy sample and paraffin combination. The average section is usually 3 μm to 5 μm thick. Usually, the technologist will take no more than about thirty slices into the biopsy and paraffin combination. The total depth into the paraffin of all of these combined sections is around 0.001 inch. Therefore, if the biopsy sample is not correctly repositioned to be perfectly flat before it is embedded in the paraffin, it is quite possible that a portion of the biopsy sample will never be sectioned and thus excluded from the pathologist&#39;s subsequent examination.  
      Many times, landmark indicators are used when taking biopsy samples. Landmark indicators indicate to the medical professional the location of harvest relative to the patient&#39;s body. The landmark indicators ensure that a follow-up can be accurately planned during a subsequent surgery, in staging of the tumor, etc. Sutures have been secured to the biopsy sample to provide one type of landmark indicator. However, sutures can be difficult and time consuming to apply. Currently, there is a need for a less time-consuming and more accurate manner to identify the orientation of the sample in relation to the patient&#39;s anatomy.  
      The present invention is directed toward addressing these and other needs.  
     SUMMARY  
      One aspect of the invention is a cassette for holding tissue. The cassette includes a first flat reference porous structure for supporting the tissue. The cassette also includes a second porous structure having a compression resistance. The first flat reference porous structure and the second porous structure can be positioned into an abutting position for securing the tissue therebetween.  
      Another aspect of the invention is a method for improving the quality of sections of a biopsy sample. The method includes placing the biopsy sample into a tissue cassette and moving at least a portion of the tissue cassette to apply a compressive force to flatten the biopsy sample against a flat reference surface of the tissue cassette.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate some embodiments and, together with the detailed description of the illustrated embodiments given below, serve to explain some embodiments covered by the claims.  
       FIG. 1  is a perspective view of a tissue cassette in an open position according to one embodiment.  
       FIG. 2  is a cross-sectional view of the tissue cassette taken generally along line  2 - 2  in  FIG. 1  but shown in a closed or latched position.  
       FIG. 3  is a perspective cross-sectional view of the tissue cassette also taken generally along line  2 - 2  of  FIG. 1  and illustrating the cassette in an open position.  
      FIGS.  4 A-C are top plan views of a landmark indication system in different uses with the tissue cassette of  FIG. 1 .  
       FIGS. 5A and 5B  are illustrations of respective first and second microscope slides comparing biopsy samples that had been previously held in a conventional biopsy container ( FIG. 5A ) and samples held with the tissue cassette of  FIG. 1  ( FIG. 5B ).  
       FIGS. 6A and 6B  are further illustrations of respective first and second microscope slides comparing biopsy samples that had been previously held in a conventional biopsy container with formalin ( FIG. 6A ) and samples held with the tissue cassette of  FIG. 1  ( FIG. 6B ).  
       FIG. 7A  illustrates a tissue sample obtained from a conventional tissue transporting or biopsy container, with the tissue positioned inside of a paraffin mold prior to embedding and sectioning.  
       FIG. 7B  illustrates a section of the tissue sample of  FIG. 7A  positioned upon a slide for diagnosis by a medical professional.  
       FIG. 8A  illustrates a tissue sample obtained from the tissue cassette of  FIG. 1 , with the tissue positioned inside of a paraffin mold prior to embedding and sectioning.  
       FIG. 8B  illustrates a section of the tissue sample of  FIG. 8A  positioned upon a slide for diagnosis by a medical professional.  
       FIG. 9  is a perspective view of a tissue cassette according to another embodiment and shown in a closed position.  
       FIG. 10  is a perspective view of the tissue cassette shown in  FIG. 9 , but illustrated prior to the securement of respective porous membranes.  
       FIG. 11  is a cross sectional view taken along line  11 - 11  of  FIG. 9 .  
       FIG. 11A  is an enlarged view of encircled portion  11 A shown in  FIG. 11 . 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS  
      The present application is directed to a cassette for transporting tissue after a biopsy has been performed. Generally, the cassette includes two opposing porous surfaces for fixing or holding tissue samples therebetween.  
      Referring now to the drawings,  FIG. 1  illustrates a tissue cassette  100 . The tissue cassette  100  is constructed and arranged to hold biopsy tissue samples after they have been removed from the patient and before the pathologist processes them for inspection. The tissue cassette  100  is therefore designed to be placed in another container (not shown) adapted to hold a tissue preservative solution, such as a formalin solution, such that the solution can fully contact the tissue cassette  100  and any tissue sample(s) therein. The tissue cassette  100  includes a first perforated structure or frame  102  and a second perforated structure or frame  104 . The terms “perforated” and “porous” are used herein as analogous or synonymous terms meant to convey the fact that fluid solution can reach the tissue through the pores or perforations of the structure. As illustrated in  FIG. 1 , the first perforated structure  102  and the second perforated structure  104  are generally of the same size and are positioned opposite from one another. This arrangement allows the first perforated structure  102  and the second perforated structure  104  to easily be brought together to apply a compressive force to the biopsy sample after it has been inserted therein. The first perforated structure  102  includes a forward surface  106 , a rearward surface  108 , and two side surfaces  110 . It also includes an outer surface  112 . The rearward surface  108 , and any other surface, can have multiple minor surfaces that taken together comprise the surface. These five surfaces  106 ,  108 ,  110 , and  112  combine together to define an interior area  114  that contains a first porous structure  116 . In some embodiments, the porous structure  116  is a foam pad, however, in other embodiments other types of materials may be used. Some types of materials for the foam pad are polyester or polyurethane with an open cell reticulated structure. Furthermore, special foams with hydrophilic properties could be used to assure wetting of intricate samples. In addition, while one porous structure  116  is illustrated inside the interior area  114  in  FIG. 1 , two or more porous structures can be used in other embodiments. In this illustrated embodiment, the interior area  114  is substantially box shaped, however, in other embodiments the first perforated structure  102  may have an interior area  114  that is different in configuration. For example, the interior area  114  could be an oval shape, a cylindrical shape, a rectangular shape, a square shape, or any other area readily apparent to those skilled in this art. Accordingly, the interior area  114  may be sized to receive a variety of biopsy sample sizes.  
      Similarly, the second perforated structure or frame  104  includes a forward surface  118 , a rearward surface  120 , side surfaces  122 , and an outer surface  124 . The combination of all these surfaces  118 ,  120 ,  122 , and  124  defines an interior area  126  that contains a second porous structure  128  that may be constructed out of foam or other materials. The perforated structures  102 ,  104  can be constructed out of a variety of materials. In the illustrated embodiment, the perforated structures  102 ,  104  are constructed out of a plastic material, such as a high-density polyethylene (HDPE) or Acetel. In other embodiments, however, other materials may be used. In addition, the porous structures  116 ,  128  may include porous membranes  130  and  132 . These porous membranes  130 ,  132  are constructed and arranged to avoid damage to the tissue sample(s) and to minimize or prevent artifacts in the tissue sample(s) so extremely small biopsy samples, such as those less than 0.5 mm in size, can be effectively secured in the tissue cassette  100 . In the illustrated embodiment, the porous membranes  130 ,  132  may be formed out of lens paper or filter paper, however, those skilled in the art will recognize that other materials can be used in other embodiments. For example, the porous membranes  130 ,  132  can be a porous material such as a thermoplastic porous film or netting, a woven or non-woven material made from cotton, or other natural or synthetic fiber materials or other suitable materials. One suitable material is sold by Delstar Technologies, Inc., Middletown, Del., under the name Delnet® and is an apertured film or netting formed from high density polyethylene, having a flat surface facing the tissue samples. One or both membranes  130 ,  132  may be eliminated as long as undesirable artifacts are not formed on the biopsy sample(s) by the porous structures  116 ,  128 . The membranes  130 ,  132  may be about 0.001 inch thick to allow unimpeded fixing fluid access and wicking action to the tissue surface. In addition, the membranes  130 ,  132  have a porosity of about 100 μm to about 400 μm some having porosity closer to about 200 μm. The membranes  130 ,  132  should remain taut and should remain temperature, moisture, and reagent stable. In addition, the membranes  130 ,  132  should not degrade when placed in the reagent solution, such as a formalin solution, and may be designed or formulated so as not to degrade when exposed to the chemicals used in the tissue processing. Furthermore, the membranes  130 ,  132  may be heat staked to the porous structures  116 ,  128  or the perforated structures  102 ,  104  or may be fixed in place by any other suitable method. The membranes  130 ,  132  need not be the same material. For instance, one of the membranes  130 ,  132  can be thinner and more compliant and conform to undulations in the biopsy sample. In addition, one of the membranes  130 ,  132  and the corresponding porous structure  116 ,  128  may be simply trapped in its perforated structure  102 ,  104  thereby allowing a free-floating configuration particularly adapted to conform to thick and thin tissue if necessary. In sum, these artifact inhibiting or minimizing porous membranes  130 ,  132  are sufficiently compliant to avoid damaging the biopsy sample, but sufficiently firm for flattening the biopsy sample before embedding in a material, such as paraffin.  
      The porous structures  116 ,  128  may have differing levels of compression resistance. Some embodiments, however, have porous structures  116 ,  128  that have the same level of compression resistance. Typically, the compression resistance ranges between about 0.5 lbs/in 2  to about 4 lbs/in 2  at about 50% compression. One porous structure  116  or  128  may be more compliant and have a compression resistance of about 0.5 lbs/in 2 . The other porous structure  116  or  128  may be less compliant with a compression resistance of about 2-4 lbs/in 2 . The porous structure  116  or  128  having the higher compression resistance can also be known as the reference structure and its corresponding porous membrane  130 ,  132  can be known as the reference surface. The typical porosity of the porous structures  116 ,  128  is around 0.020″ to 0.025″ open cell pores. In addition, in some embodiments, polyurethane foam with a hydrophilic-formulation can be used without a porous membrane if the wetting is great enough and the pore size is small enough. Moreover, the porous structures  116 ,  128  should be formed out of a material that does not degrade in the formalin or, in some cases, the chemicals used in the tissue processing. The smaller pore size would trap the biopsy sample in the tissue cassette  100  and the enhanced wetting properties would overcome the potential disadvantage of the smaller pore size.  
      In the illustrated embodiment, the second porous structure  128  has more compression resistance than the first porous structure  116 . Accordingly, when a biopsy sample is introduced into the tissue cassette  100 , the porous structure  128  having higher compression resistance will provide resistance to deformation upon closing of the tissue cassette  100 . Therefore, the flat surface of the biopsy sample will be created along the surface of the biopsy sample that is in contact with the porous membrane  132  and the second porous structure  128 .  
      The tissue cassette  100  also includes a connector system made up of a compliant hinge  135  and a clasp  136 . Those skilled in the art, however, recognize that other connector systems can be used in other embodiments. For example, in one alternative embodiment, the connector system could be two clasps that lock together on either side of the tissue cassette  100 . Moreover, in another embodiment, the connector system  134  could be elastic bands that wrap around the periphery of the perforated structures  102 ,  104 . Accordingly, any structure that can be used to urge the porous structures  116 ,  128  together is contemplated. In addition, not all tissue cassettes require a connector because the resilient porous structures  116 ,  128  could apply sufficient force in some other manner not requiring a connector.  
      The compliant hinge  135  is coupled to the first perforated structure  102  at the rearward surface  108 . The compliant hinge  135  is also coupled to the second perforated structure  104  at the rearward surface  120 . This arrangement provides a “clam shell” like design that allows the first perforated structure  102  and the second perforated structure  104  to be easily separated from one another and to easily clamp down. Moreover, this arrangement allows for a maximum separation between the forward end surfaces  106  and  118  of the first and second perforated structures  102  and  104 . This arrangement enables a user to easily place the biopsy sample inside the interior areas  114  and  126  using the harvesting instrument, and, if necessary, a portion of the medical professional&#39;s hand.  
      The clasp  136  illustrated in  FIG. 1  is one structure that can assist in coupling the perforated structures  102 ,  104 , however, those skilled in the art recognize that other mechanisms can be used so long as they provide for a compressive force to be applied to the biopsy sample upon closure. The clasp  136  of the illustrated embodiment has a top portion  136   a  and a bottom portion  136   b . The top portion  136   a  provides a latch  138  at the end of the top portion  136   a . This latch  138  slides over a bar  140  located on the bottom portion  136   b , and then retracts around the bar  140  to firmly lock into place. In addition, the top portion  136   a  includes a tab  142  which allows the medical professional to easily open the tissue cassette  100  when needed by simply pressing their thumb or finger to the underside of the tab  142  in order to retract the latch  138  from underneath the bar  140 . The clasp  136  forces the opposing porous surfaces  116 ,  128  together so as to apply a compressive force to the biopsy sample that is placed therein. The clasp  136  also includes the latch  138  and bar  140  to maintain that compressive force constantly and uniformly until the tissue cassette  100  is opened and the biopsy sample is ready to be embedded in a material, such as paraffin.  
       FIGS. 2 and 3  respectively illustrate the biopsy cassette  100  in closed and open positions. Outer surface  112  is shown to have a plurality of pores  144 . These pores  144  allow for introduction of the fixing solution, such as formalin. The porous structures  116 ,  128  allow the fluid to reach the porous membranes  130 ,  132  so that the biopsy sample can become fixed in its flattened and undamaged state. Therefore, the tissue cassette  100  prepares the biopsy sample for inspection.  
      In use, the tissue cassette  100  operates to properly flatten and leave undamaged a biopsy sample placed therein. Initially, a medical professional performs a biopsy on a patient to obtain a biopsy sample. This is usually done using a needle or other hollow instrument in order to obtain a biopsy sample inside of the lumen defined in the needle or other instrument. The biopsy sample is then taken directly to the tissue cassette  100  where it is placed on one of the porous membranes  130 ,  132 . At this point, the biopsy sample may not be flat. It could be coiled or contorted in any number of configurations.  
      The tissue cassette  100  is then closed and the porous membranes  130 ,  132  may apply uniform and constant pressure to the biopsy sample. The differences in compression resistance between the porous structures  116 ,  128  result in one of the sides of the biopsy sample becoming flattened. The second porous structure  128  having a higher compression resistance will not compress substantially and the first porous structure  116  will compress so as not to damage the biopsy sample and introduce artifact therein. The first porous structure  116  may surround all sides of the tissue sample except the side which is against the second porous structure  128 . Flattening of one side of the tissue sample can occur due to one of the porous membranes  130  or  132  being taut. In addition, the other porous membrane  130  or  132  can be free-floating inside of its perforated structure  102 ,  104 , either by not being heat staked and simply resting upon a porous structure  116  or  128  or by being fixed only to the porous structure  116  or  128  and not fixed to the perforated structure  102 ,  104 . Likewise, the porous structure  116  and/or  128  may or may not be fixed to the associated perforated structure  102 ,  104 . Accordingly, the biopsy sample may be flattened and fixed to prevent curling or distortion of the biopsy sample and a loss of visible margins.  
      Tissue cassette  100  may be immersed in a container filled with a fixing solution. The biopsy sample can then be hardened with one side flat and without visible artifact. Having a flat surface can be especially important for skin biopsy samples. The tissue cassette  100  can thereafter be stored until it is ready to be opened by a medical professional. Use of tissue cassettes  100  may allow a biopsy sample to be held flat, for example, within less than a 0.0025 inch variance. This level of precision can be important for skin tissue biopsies because the samples do not curl up and distort the margins for excision of malignant tissue. Therefore, when the technologist introduces the biopsy sample into the paraffin and then makes slices using a microtome, the possibility that an incorrect diagnosis due to curling or distortion of the biopsy sample is reduced because the margin intended by the surgeon or other medical professional taking the sample is properly preserved throughout the histological process. The pathologist has the assurance that the margin that will be delivered back to the harvesting medical professional will be as the medical professional intended.  
      Referring now to FIGS.  4 A-C, a landmark indication system  146  may be used on, for example, the porous membrane  132  associated with the porous structure  128  of greater compression resistance. The medical professional that harvests the biopsy sample places the biopsy sample on the porous membrane  132  and uses the landmark indication system  146  to communicate the anatomic position of the harvested tissue or other information concerning the biopsy sample. The landmark indication system  146  includes four quadrants  148  that are identified using labels  150 . Illustrative examples are provided in FIGS.  4 A-C discussed below. FIGS.  4 A-C illustrate some uses of the landmark indication system  146 , however, those skilled in this art recognize that the landmark indication system  146  can be used in other manners.  
      Referring now to  FIG. 4A , the landmark indication system  146  is used with biopsy samples  152  and  154  taken from a prostate gland. The biopsy samples  152  and  154  represent prostate cores harvested by a medical professional during a biopsy. Biopsy samples  152  illustrate cores harvested from the left side of the prostate gland. Accordingly, the “Left” label  150  is circled to make this indication. Similarly, the biopsy samples  154  are taken from the right side of the prostate gland and the “Right” label  150  is accordingly circled. Thus, the histotechnician or other medical profession will be able to label the paraffin sections to accurately reflect the area of the prostate where the cores were harvested.  
       FIG. 4B  illustrates another use of the landmark indication system  146 . In the center of the landmark indication system  146  is a skin tissue sample  156  taken from a finger. The skin tissue sample  156  includes a lesion  158 . The orientation of the skin tissue sample  156  is identified by circling the “Proximal” and “Distal” labels  150  as illustrated in  FIG. 4B . Again, this system enables the medical professional harvesting the skin tissue sample  156  to easily communicate the orientation of the skin sample, relative to the proximal and distal ends of the patient&#39;s finger. Thus, the likelihood of error decreases.  
       FIG. 4C  illustrates the landmark indication system  146  for use with taking a multitude of biopsy samples  160 . The tissue cassette  100  will keep the biopsy samples  160  in place once it is closed. Thus, the medical professional, such as a surgeon, can create a surgical report and make notes under the heading of quadrant “1” corresponding to the label  150  of “1” that is circled. Such notes can describe characteristics of those samples. For instance, assume that the samples  160  in the quadrant  148  having the “1” label  150  are all from the pancreas. In addition, assume a biopsy was also taken from the gall bladder, kidney, and liver. The samples  160  can be organized in the quadrants  148  and then the labels  150  corresponding to the numbers can be circled. The surgical report can be written by the surgeon to provide information noting that the samples  160  in the quadrant  148  with the label  150  having “1” were taken from the pancreas, those under “2” from the gall bladder, and so forth. Thus, the landmark indication system  146  can provide information to the pathologist or histotechnician in many different manners.  
      The pathologist and the histotechnician can use information from labels  150  communicated by the medical professional when subsequently preparing the gross description. The gross description is prepared by the histotechnician or the pathologist opening the tissue cassette  100  and observing the number, placement, size, and/or anatomic orientation indicated by the medical professional who harvested the tissue. Subsequently, the tissue cassette  100  can be closed for further tissue processing without the need for additional manipulation of the biopsy sample before embedding. The tissue cassette  100  completely preserves the orientation of the biopsy sample throughout the entire tissue fixing process.  
      To perform an embedding process the histotechnician or the pathologist removes the biopsy sample from the tissue cassette  100 . The landmark indication system  146  makes the anatomic harvest position easily identifiable and able to be oriented and processed into standard embedding molds. Alternatively, when using a system having a sectionable cassette, the tissue cassette  100  keeps the biopsy sample flat and indicates the harvested orientation of the biopsy samples using the landmark indicator system  146 . The tissue is prefixed and substantially hardened before removing it from the tissue cassette  100  and placing it into a sectionable cassette, other support, embedding medium mold, etc.  
      Referring now to  FIGS. 5A and 5B , and  FIGS. 6A and 6B , first slides  162 ,  164  shown respectively in  FIGS. 5A and 6A  illustrate biopsy samples taken from a conventional tissue preservative container and freely submerged in the preservative solution. The second slides  166 ,  168  shown respectively in  FIGS. 5B and 6B  illustrate biopsy samples taken from the tissue cassette  100  which was then submerged in the preservative solution. The second slides  166 ,  168  illustrate samples that are defined and have full width. The robustness of the sections of the slide is improved. Accordingly, the tissue cassette  100  greatly reduces the margin of error during embedding a biopsy sample for later diagnosis.  
       FIG. 7A  illustrates a mold  170  for holding a biopsy sample  172  during embedding with a material such as paraffin wax. The mold  170  receives the biopsy sample  172  after sample  172  has hardened into the configuration illustrated. The biopsy sample  172  is convoluted and includes high points  174  and low points  176 . After embedding the biopsy sample  172  in paraffin wax, a plurality of sections can be taken through the biopsy sample  172  using a microtome. The line  178  illustrates the most common area that a section will be taken through the biopsy sample  172 . The biopsy sample  172  includes a lesion  180 , such as a group of cancerous cells. The line  178  is below the lesion  180 . Referring to  FIG. 7B , the section taken through line  178  is illustrated as being placed upon a slide  182 . Three sections of the tissue sample  172  are located on the slide  182 . The first section  172   a  corresponds to the length of the biopsy sample  172  between points A and B illustrated in  FIGS. 7A and 7B . The second section  172   b  corresponds to the length of the biopsy sample  172  between points C and D. The third section  172   c  corresponds to the length of the biopsy sample between points E and F. The lesion  180  does not appear because it is between points D and E close to a high point  174 . Accordingly, the diagnosis will be inaccurate.  
      Referring now to  FIG. 8A , a biopsy sample  172 ′ has been taken from the tissue cassette  100  of  FIG. 1  and placed into a mold  170 . After placing the biopsy sample  172 ′ into the mold  170 , the biopsy sample  172 ′ is embedded in a material such as paraffin wax. Sections are then taken with a microtome, such as through line  178 . The tissue cassette  100  of  FIG. 1  has formed the biopsy sample  172 ′ flat so the line  178  passes through the lesion  180 ′.  FIG. 8B  illustrates that the medical professional places the section taken through line  178  upon the slide  182  in preparation for diagnosis. The biopsy sample  172 ′ has a flat section  172   a ′ that is visible along the entire length of the biopsy sample  172 ′. Accordingly, the section of the lesion  180   a ′ appears inside of the flat section  172   a ′ and will be discovered by the pathologist or other medical professional. Thus, the tissue cassette  100  helps ensure that the proper diagnosis of a biopsy sample  172  is performed.  
      Referring now to  FIGS. 9-11  and  11 A, a tissue cassette  100 ′ is shown according to a second illustrative embodiment. The tissue cassette  100 ′ may include any of the features discussed above with respect to the first embodiment. Certain differences exist between the first and second embodiments as will be apparent from the following description and a review of the respective drawing figures. Like reference numerals with prime marks (′) are used to illustrate corresponding elements in the first and second embodiments with structural and/or functional differences being apparent from a review of the respective drawing figures, the written description, or both. The tissue cassette  100 ′ comprises first and second perforated structures, including a lid  102 ′ and a base  104 ′ which may be connected by a hinge  135 ′ at one end and a clasp structure  136 ′ at the opposite end. Apertures  144 ′ are provided to allow fluid flow into the cassette  100 ′. The clasp structure may comprise a projection  136   a ′ on the lid  102 ′ received within a recess  136   b ′ on the base  104 ′. The lid  102 ′ also includes a second clasp structure  236  adjacent to the hinge  135 ′. This clasp structure  236  comprises a projection  236   a  and a recess  236   b  as best shown in  FIG. 10  in the open position and  FIG. 11A  in the closed position. As the lid  102 ′ is closed, the hinge, which is frangible, breaks and the clasp structure  236  engages to hold the lid  102 ′ to the base  104 ′ in the closed position along with clasp structure  136 ′ as shown in  FIGS. 11 and 11 A. Sidewalls  240 ,  242  of the lid  102 ′ are received within complementary receiving areas  246 ,  248  of the base  104 ′ ( FIG. 10 ). Therefore, in the closed position shown in  FIG. 9 , tissue samples are prevented from escaping from the sides of the cassette  100 ′ as well as the ends of the cassette  100 ′ having the respective clasp structures  136 ′,  236 . A tab  200  on the lid  102 ′ may be used to apply upward force on the lid  102 ′ to decouple the clasp  136 ′.  
      As shown in  FIGS. 11 and 11 A, porous membranes  130 ′,  132 ′ may be heat staked to the perforated structures  102 ′,  104 ′ through the use of projections  202 . These projections  202  are shown in  FIG. 10  prior to the heat staking operation as small cylindrical elements. After heat staking, the cylindrical elements  202  form mushroom-shaped heads which retain the edges of the membranes  130 ′,  132 ′ against the upper surfaces of the porous structures or foam  116 ′,  128 ′. As further shown in  FIGS. 11 and 11 A, a fluid path may be formed completely between the first and second perforated structures  102 ′,  104 ′ such that fluid (such as formalin) may travel between the lid  102 ′ and base  104 ′ in the direction of the arrow  203  shown in  FIG. 11A . The fluid path extends between additional portions  102   a ′,  102   b ′,  104   a ′,  104   b ′ of the perforated structures  102 ′,  104 ′ and between the “mushroomed” projections  202 . Projections  202  may be staggered relative to each other when the lid  102 ′ is closed instead of aligned as shown in  FIG. 11A . This fluid path allows full saturation of the tissue sample(s). A spacing  204  is also shown between the upper and lower porous membranes  130 ′,  132 ′. The spacing  204  may or may not be present depending on the needs of a particular application. For example, larger tissue samples may require a spacing  204  of any suitable dimension that will still allow the sample to be properly held, while smaller specimens may require no spacing  204 .  
      It should further be noted that a nonstick coating may be applied to one or both of the porous membranes  130 ′,  132 ′ such that the tissue sample or samples may be easily removed from the surface  130 ′ or  132 ′ having a nonstick coating. Alternatively, the membrane material itself may comprise a nonstick-type material such as PTFE. As another alternative, one or more tissue samples may be adhesively secured on one of the porous membranes  130 ′ or  132 ′ so as to retain the sample(s) on the membrane  130 ′ or  132 ′. After fixing with a fluid such as formalin, the membrane having the adhesively secured tissue sample or samples may be cut out of the cassette  100 ′ and placed in the bottom of an embedding mold or sectionable cassette for embedding in a material such as paraffin. Whether the tissue sample or samples are adhesively secured to one of the membranes or not, the lid  102 ′ may be entirely removed from the base  104 ′ and discarded either before or after the biopsy sample or samples are retrieved. The biopsy sample or samples may be placed in the bottom of a conventional paraffin mold and the mold may be filled with molten liquid paraffin. While the paraffin is still molten, the base  104 ′ may be placed into contact with the paraffin. The paraffin then cools and hardens. The base  104 ′ may then be used as a fixture for retention in a microtome chuck. A microtome operation may then be performed on the hardened paraffin and slide preparation and analysis may take place.  
      While these embodiments have been described in considerable detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The claims are not, therefore, limited to the specific details of the representative system, apparatus, and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicant&#39;s claims.