2.3 Specimen Accessioning, Grossing & Special Tissue Handling

2.3 Specimen Accessioning, Grossing & Special Tissue Handling

The pre-analytical phase of histology begins the moment tissue is excised. Meticulous accessioning, container verification, gross examination, margin inking, and tissue-specific grossing protocols form the foundation of anatomical pathology. Pre-analytical errors are frequently irreversible and jeopardize patient safety.

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Specimen Accessioning and Identification Integrity

Accessioning logs surgical specimens into the laboratory information system (LIS), assigning a permanent surgical pathology accession number.

Identification and Verification Mandates

Accrediting agencies (CAP, Joint Commission, CLSI) enforce strict standards:

• Two Unique Patient Identifiers: Every container and requisition must display at least two matching identifiers (patient name, date of birth [DOB], or medical record number [MRN]). Room or bed numbers are invalid.
• Requisition Reconciliation: Verifies matching patient identifiers, anatomical site with laterality, clinical history, submitting physician, collection time, and container count.
• Container Labeling Mandate: Labels must be affixed to the container body, NEVER the lid. Lids are removed during grossing and can be inadvertently swapped.
• Discrepancy Quarantine: Any labeling mismatch or unlabeled specimen requires immediate quarantine. Tissue must not be grossed or processed until resolved with the clinical team.

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Surgical Margin Inking Techniques and Mordanting

Margin evaluation determines whether a neoplasm has been excised with clear margins (R0) or extends to the cut edge (R1 microscopic margin), guiding re-excision or adjuvant therapy.

Application Technique

1. Surface Preparation: Orient and blot thoroughly dry with gauze. Applying ink to wet or bloody surfaces causes pigment to run and fail to adhere.
2. Ink Application: Acrylic margin dyes or India ink are applied sparingly to true surgical margins.
3. Chemical Mordanting: Set with a mordant to prevent bleeding during processing:
   • Bouin's solution (acetic and picric acids precipitate binders)
   • Dilute (3%–5%) acetic acid
   • 70%–100% isopropyl alcohol Reacting for 1 to 2 minutes bonds pigment to outer fascia or capsule.
4. Multi-Color Margin Coding: Standardized colors differentiate anatomical orientations (e.g., Superior = Blue, Inferior = Green, Anterior = Yellow, Posterior = Orange, Medial = Red, Lateral = Black, Deep = Violet). Gross records must document each assigned color.

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Grossing Principles: Bread-Loafing and Cassette Selection

Tissue Bread-Loafing

Solid organs, large tumors, and resections (mastectomies, colectomies, uteri, spleens) must be bread-loafed upon receipt:

• Slicing Technique: Serially sliced at uniform 3 to 5 mm intervals perpendicular to the long axis, leaving tissue intact on one edge like book pages to preserve orientation.
• Penetration Dynamics: Formaldehyde penetrates tissue at ~1.0 mm/hr initially ($d = K \sqrt{t}$). Uncut solid organs suffer central autolysis. Serial slicing ensures rapid, uniform fixative penetration.

Cassette Selection and Loading

• Trimming Dimensions: Routine sections should measure ~20 × 25 mm and must not exceed 3 mm in thickness. Thicker slices compress tissue and impede fluid exchange.
• Standard Cassettes: Used for routine specimens. Tissue should occupy no more than 75% of cassette volume.
• Biopsy Enclosures: Endoscopic biopsies, needle cores, and curettings wash out through standard cassette vents. Delicate specimens require:
  • Fine-mesh biopsy cassettes
  • Nylon biopsy bags
  • Folded lens/biopsy paper
  • Foam biopsy pads (pre-moistened with 10% NBF to prevent adherence artifacts)

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Tissue-Specific Handling Guidelines

Breast Biomarker Guidelines (ASCO/CAP)

ASCO and CAP enforce strict standards for breast cancer biomarkers (ER, PR, HER2/neu):

1. Cold Ischemic Time: Must be recorded and kept <1 hour (<60 min) to prevent receptor degradation.
2. Fixation Window: Strictly 6 to 72 hours in 10% NBF. Under-fixation (<6 hr) yields false-negative ER/PR; over-fixation (>72 hr) causes epitope masking and false-negative HER2.
3. Gross Handling: Resections must be bread-loafed at 5 mm and interleaved with paper towels in formalin (≥10:1 ratio).

Specialized Handling Pearls

• Lymph Nodes: Touch imprints for rapid cytodiagnosis; submit fresh tissue in RPMI 1640 on wet ice for flow cytometry.
• Bone Biopsies: Complete formalin fixation is mandatory before acid decalcification to prevent nuclear bubbling and marrow loss.
• Cytology Blocks: Clotting with plasma-thrombin, agar embedding, or formalin pellets preserves micro-architecture.

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Fixation and Processing for Molecular Testing and In Situ Hybridization

In situ hybridization is listed under both Fixation and Processing in the ASCP BOC content outline, and the histotechnician controls almost every variable that determines whether a FISH or CISH assay produces a readable signal.

• Fixative: 10 percent neutral buffered formalin only. Acidic and heavy-metal fixatives - Bouin, B-5, Zenker, Helly - fragment DNA, quench hybridization signal, and inhibit downstream amplification. A block fixed in B-5 cannot be rescued for FISH.
• Cold ischemic time: keep under 1 hour. RNA degrades faster than DNA, so RNA-based assays such as RNA in situ hybridization are the least forgiving of delay.
• Fixation window: 6 to 72 hours matches the ASCO/CAP breast biomarker requirement and is the practical window for FISH as well. Prolonged fixation beyond about 72 hours progressively reduces probe penetration and signal intensity.
• Decalcification: EDTA only. Strong acid decalcification hydrolyzes nucleic acid and destroys FISH targets in bone and marrow specimens.
• Processing and embedding: keep paraffin at or below 60 degrees C; excessive heat in the infiltration bath or the slide oven degrades nucleic acid. Use validated clearing agents; unvalidated xylene substitutes leave residues that interfere with probe access.
• Sectioning: cut at 4 to 5 micrometres onto positively charged slides. Use a fresh blade and clean, fresh flotation bath water for each molecular case to avoid carrying a floater from one patient into another's hybridization result.
• Section age: unstained slides deteriorate. Cut sections as close to the assay as possible rather than banking them for months.
• Contamination control: handle slides for RNA assays with gloves and clean instruments; skin ribonuclease is sufficient to destroy an RNA target.
• Cytology material is acceptable: alcohol-fixed smears and formalin-fixed cell blocks both support FISH when the cellularity is adequate.

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ASCP BOC Exam Traps & Clinical Scenarios

[!CAUTION] Exam Trap 1: The ASCO/CAP Breast Fixation Window Breast tissue fixed 84 hours over a weekend violates ASCO/CAP 72-hour limits, causing epitope masking and false-negative HER2 testing. Protocol deviations must be formally documented.

[!WARNING] Exam Trap 2: Acid Decalcification of Unfixed Bone Placing fresh bone directly into 10% nitric acid causes marked marrow autolysis, nuclear chromatin bubbling, and loss of hematoxylin basophilia. Bone must always be fully fixed in formalin prior to acid decalcification.