Brain and Spinal Cord
In some respects, pathologic evaluation of speci-mens from the central nervous system (CNS) is less complicated than evaluation of other or-gans, because requests for margins and the need for extensive specimen dissections are unusual. On the other hand, CNS specimens are usually small, and care must be taken to preserve the tis-sue. Do not use all of the tissue by freezing the entire specimen. This is especially true for speci-mens of the spinal cord. These can be minute, yet major therapeutic decisions often depend on the results of the pathology studies. In all cases, it is essential to keep the clinical and radiologic findings in mind when processing specimens from the CNS.
Ultrasonic aspirations are widely used for tumor resections. As a consequence, much of the specimen may be lost unless it is recovered from the instrument’s bag receptacle. The fragments may be difficult to interpret histologically but can be invaluable. They are entirely suitable for molecular or cytogenetic studies.
Cytologic preparations are essential in the frozen section and permanent section evaluation of all surgically excised brain lesions. These should be prepared in every case for which a frozen section is requested. As illustrated, the preferred proce-dure is as follows: A minute portion of the fresh specimen is placed on a glass slide and, with con-siderable pressure, smeared between an oppos-ing slide. The slides are separated and immersedimmediately in 95% alcohol. Following fixation for45 to 60 seconds, the preparation is stained and coverslipped. I prefer routine staining with hema-toxylin and eosin.
Needle biopsy specimens need to be interpreted and handled with special care. The evaluation should begin with cognizance of the clinical and radiographic findings. The chance of making an error is vastly increased when these specimens are studied in a vacuum devoid of clinical or radiographic information.
Begin your examination with the cytologic preparation as described above. One of the re-maining fragments of tissue can then be used for a frozen section if desired. If an abnormality is established by the smear, a frozen section may not be necessary. Unless you are assured of addi-tional tissue, it is generally wise to freeze only one or two cores at the time of initial examination, holding others in reserve. Throughout the pro-cess, review these slides in reference to the ra-diographic images to ensure that abnormal tissue is obtained and that the findings are consistent with the images. Close contact with the surgeon is extremely important. As is true for biopsies from other body sites, small specimens can be colored with eosin to facilitate identification at the time of embedding and sectioning.
Freezing must be accomplished as rapidly as pos-sible to minimize the formation of ice crystals.
Ice crystals are generally avoidable in certain neo-plasms, such as meningiomas, but frequently not in infiltrating gliomas from edema-rich white matter. The recommended procedure is to estab-lish a base of semifrozen mounting medium on a cold chuck. The medium should not be com-pletely frozen, because solidly frozen medium will slowly freeze the tissue and encourage the formation of ice crystals by gradually drawing heat from the small specimen. Therefore, place the specimen on the partially frozen base, and immediately immerse it in liquid nitrogen. After freezing, the specimen can then be covered with additional mounting medium and refrozen. Cut and stain sections by standard methods.
In the case of gliomas, especially the well-differentiated variety (e.g., astrocytoma and oli-godendroglioma), it is extremely important that blocks be available from tissue that is not subject to prior frozen section. Prior freezing produces nuclear angulation and hyperchromatism, which can make it difficult to distinguish between glio-mas and to distinguish reactive or normal brain from an infiltrating glioma. Unless you are as-sured of more tissue by the surgeon, use only a portion of the specimen for a frozen section.
To a large extent, immunohistochemistry has re-placed electron microscopy as a diagnostic tool; however, in certain instances the latter technique is invaluable. Accordingly, it is appropriate to hold some tissue in reserve in glutaraldehyde (embedding later if necessary) for neoplasms for which classification may be difficult after review of the frozen section. Tissue may also be embed-ded from encephalitic lesions if viruses are sus-pected, because no immunohistochemical agents are commercially available for many classes of potential viral pathogens.
Meningiomas are frequently submitted with a dural attachment and arrive as either a complete en bloc excision or, more often, as a series of small fragments. Prognostically significant informationrelates to histologic features of the lesion as well as the interface of the tumor with surrounding tissues, that is, the brain and the skull. The surface of the mass adjacent to the brain should be sec-tioned, if identified, particularly if portions of the brain adhere to the surface. At least one section through the base of the tumor on the dura should also be taken. Decalcified sections of bone are appropriate to evaluate skull invasion.
Gliomas are an exceedingly heterogeneous group in terms of their macroscopic and micro-scopic characteristics. Generally, margins are not an issue and do not, unless specifically stated by the surgeon, affect the treatment of the patient. Fragments of ependymomas, oligodendroglio-mas, and astrocytomas, in which little normal brain is recognized, do not need to be sampled in regard to the extent of the disease, although it is prudent to attempt such a localization. In larger en bloc specimens of gliomas, however, a series of marked and recorded sections passing from the tumor into the macroscopically normal brain is appropriate. In the case of malignant gliomas with central necrosis, the most diagnostic tissue is usually found in the cellular rim immediately surrounding the necrotic area. Sections from this area are therefore appropriate. In the case of well-differentiated gliomas (e.g., astrocytoma and oligodendroglioma), the tissue may not appear markedly abnormal, and multiple sections are necessary, particularly from areas in which the white matter is discolored.
Malignant gliomas after radiotherapy may have extensive therapy-related changes, such as coagulation necrosis. In this setting, multiple tissue sections should be submitted so as not to miss potential foci of active recurrent tumor.
Oligodendrogliomas are increasingly diag-nosed by molecular techniques. The molecular laboratory can be consulted in regard to specific tissue preparation (e.g., fresh frozen, etc...).
Lymphomas are generally recognized during the frozen section process and, in the sporadic form in the nonimmunocompromised patient, they are often suspected on the basis of the neuroimaging features. In this setting, tissue can be reserved frozen for special marker studies, although most of the relevant markers for the simple purpose of establishing a clinical diagnosis can be performed on paraffin-embedded sections. A clinical history of prebi-opsy steroid treatment is significant, as CNS lymphomas in this setting may be little more thana mass of macrophages and few if any residual neoplastic cells.
Pituitary adenomas are often approached via the transsphenoidal route, and the specimens are often small. Care must be taken not to freeze all of the specimens, as the resultant artifact complicates interpretation of permanent sections. Close com-munication with the surgeon is essential.
Creutzfeldt-Jakob disease is a rare disorder that is occasionally diagnosed in a cortical biopsy specimen. Although there appears to be only a very small likelihood that pathology person-nel will contract Creutzfeldt-Jakob disease from these specimens, caution is appropriate consider-ing the devastating consequences of this disease. Details of this issue are discussed by Brown.20Basically, the tissues are fixed in a standard for-malin solution for at least 48 hours. The tissues are then placed in a cassette and decontaminated by immersion with periodic agitation in a 95% formic acid solution. The tissue will turn clear. After this, the tissue is placed in formalin again for 1 to 2 days. The tissues can then be treatedas any other routine specimen, although some laboratories prefer to hand process them sepa-rately. Generally, frozen sections are not recom-mended on tissues from demented patients.
Specimens taken to control seizures are usually from the temporal lobe. Often they consist of “lateral” and “medial” temporal lobe specimens. The latter contains the hippocampus, which must be examined carefully for the presence or absence of “mesial” or “hippocampal” sclerosis (i.e., neu-ronal loss and gliosis).
• What procedure was performed?
• What are the type and grade of the neoplasm? (For glial neoplasms, be sure to document the grading system employed.)
• What is the size of the neoplasm?