(rhabdomyosarcomas, neuroblastomas, peripheral neuroectodermal tumors [PNET]), that demonstrate characteristic translocations. Based on the results, treatment can be directed and prognostic features associated with certain mutations and translocations.
Hicks J, Mierau GW. The spectrum of pediatric tumors in infancy, childhood, and adolescence: a comprehensive review with emphasis on special techniques in diagnosis. Ultrastruct Pathol. 2005;29(3-4):175–202.
Oostlander AE, Meijer GA, Ylstra B. Microarray-based comparative genomic hybridization and its applications in human genetics. Clin Genet. 2004;66(6):488–495.
Diagnostic Electron Microscopy
Diagnostic electron microscopy (DEM) is used primarily to indicate the cell of origin of a tumor of questionable differentiation rather than to distinguish between benign and malignant processes. Although immunopathologic studies are less expensive and performed more rapidly than DEM, in some cases, DEM complements immunopathologic studies. The surgeon should consult with the pathologist before surgery to determine whether DEM might play a role in the study of a particular tissue specimen.
Special Techniques
Fine-Needle Aspiration Biopsy
Fine-needle aspiration biopsy (FNAB) has been used instead of excisional biopsy by nonophthalmic surgeons and pathologists. It is especially useful if the physician performing the biopsy can grasp the lesion (usually between the thumb and forefinger) and make several passes with the needle to obtain representative areas. The use of FNAB (with the results interpreted by a well-trained cytologist or ophthalmic pathologist) is becoming more common in ophthalmology.
Intraocular FNAB may be useful in distinguishing between primary uveal tumors and metastases, and biopsy specimens can undergo genetic analysis using a microsatellite assay in order to identify monosomy 3 in uveal melanoma, which would indicate a poor prognosis. Intraocular FNAB has also been utilized in the diagnosis of primary intraocular lymphoma, and the biopsy specimens can undergo flow cytometric analysis, immunocytologic analysis, cytokine analysis, or molecular biological analysis (using PCR on both fixed and nonfixed material). Special fixatives are used for cytology specimens.
The procedure is performed under direct visualization through a dilated pupil. Iris tumors may be accessible for FNAB during slit-lamp biomicroscopy. However, FNAB alone cannot reliably predict the prognosis of a uveal melanoma because the sample with intraocular FNAB is limited. Intraocular FNAB may also enable tumor cells to escape the eye; this possibility is an area of some controversy. In general, properly performed, FNAB does not pose a significant risk for seeding a tumor, but retinoblastoma is a notable exception. FNAB of a possible retinoblastoma lesion, if indicated, should be performed by an ophthalmic oncologist with ample experience in making the diagnosis and performing the procedure.
The cells obtained through FNAB can be processed through cytospin of fluid or preparation of a cell block (Fig 4-7). Cell block allows the pathologist to employ special stains, immunohistochemistry, in situ hybridization, microarray, and gene expression profiling, if needed.
Some orbital surgeons have used FNAB in the diagnosis of orbital lesions, especially presumed metastases to the orbit and optic nerve tumors. However, because it is difficult to make several passes
at different angles through an intraorbital tumor, FNAB of orbital masses may not adequately sample representative areas of the tumor. Specific indications for when and when not to perform intraocular or intraorbital FNAB are beyond the scope of this discussion, but some of these indications are discussed in Part II of this book, Intraocular Tumors: Clinical Aspects. Ophthalmic FNAB should be performed only when an ophthalmic pathologist or cytologist experienced in the preparation and interpretation of these specimens is available.
Cohen VM, Dinakaran S, Parsons MA, Rennie IG. Transvitreal fine needle aspiration biopsy: the influence of intraocular lesion size on diagnostic biopsy result. Eye. 2001;15(Pt 2): 143–147.
Frozen Section
Permanent sections (tissue that is processed after fixation through alcohols and xylenes, embedded in paraffin, and sectioned) are always preferred in ophthalmic pathology because of the inherent small size of samples. If the lesion is too small, it could be lost during frozen sectioning. A frozen section (tissue that is snap-frozen and immediately sectioned in a cryostat) is indicated when the results of the study will affect management of the patient in the operating room. For example, the most frequent indication for a frozen section is to determine whether the resection margins are free of tumor, especially in eyelid carcinomas. Appropriate orientation of the specimen, correlated with documentation (through drawings of the excision site, labeled margins, or margins of the excised tissue that are tagged with sutures or other markers), is crucial when tissue is submitted for margin evaluation.
Figure 4-7 Fine-needle aspiration biopsy (FNAB) of choroidal tumor. A, Cytologic liquid-based preparation displays prominent nucleoli (arrow) and some brown pigment (arrowhead) suggestive of melanoma. B, Cell block of the aspirated cells, stained with HMB-45 using a red chromogen, is positive, confirming the diagnosis of melanoma. Notice the difference between the red chromogen (arrows) and the brown melanin (arrowheads). (Courtesy of Patricia Chévez-Barrios, MD.)
Two techniques are used for assessing the margins in eyelid carcinomas (basal cell carcinoma, squamous cell carcinoma, and sebaceous carcinoma): routine frozen sections and Mohs micrographic surgery. Mohs surgery preserves tissue while obtaining free margins. Eyelid lesions, especially those located in the canthal areas, require tissue conservation to maintain adequate cosmetic and functional results. Other frequent indications for frozen sections are to determine whether the surgeon has obtained, through biopsy, representative material for diagnosis (especially
metastasis) and to submit fresh tissue for flow cytometry and molecular genetics (eg, cancers). Frozen sections are a time-intensive and costly process and should be used with discretion.
It is considered inappropriate to order frozen sections and then to proceed with a case before receiving the results from the pathologist. To ensure adequate understanding of the case and facilitate the best possible results for the patient, the surgeon should communicate with the pathologist ahead of time if a frozen section is anticipated.
Chévez-Barrios P. Frozen section diagnosis and indications in ophthalmic pathology. Arch Pathol Lab Med. 2005;129(12):1626– 1634.