# Biopsy Processing Errors and Artefacts

> Processing errors in NEET-PG Pathology: crush and cautery artefact, fixation faults, floaters, formalin pigment and failed immunohistochemistry.

- Canonical URL: https://prepelephant.com/topics/neet-pg/pathology/biopsy-processing-errors
- Exam / course: NEET-PG · Subject: Pathology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Biopsy Processing Errors and Artefacts", PrepElephant, https://prepelephant.com/topics/neet-pg/pathology/biopsy-processing-errors

## Direct answer

Artefact, not disease, generates most diagnostic trouble on a biopsy: procurement damage (crush from forceps, cautery, drying), fixation faults (delay causing autolysis, under-fixation losing antigens, over-fixation cross-linking proteins), processing failures (incomplete dehydration), microtomy defects (folds, chatter, thick sections, floaters) and staining errors. Each leaves a signature — crush turns small blue cells into uninterpretable smudges, cautery homogenises margins, formalin pigment deposits brown granules, and tissue floaters plant another patient's fragment on the slide. Downstream assays die quietly too: immunohistochemistry and HER2 in-situ hybridisation are unreliable if breast tissue is fixed outside the six-to-seventy-two-hour window, and strong-acid decalcification destroys DNA for molecular work.

## What you must remember

- **Crush artefact:** forceps-squeezed cores obliterate nuclear detail, worst in lymphomas and small round blue cell tumours; prevent it by letting tiny biopsies adhere to paper or gauze and never pinching them.
- **Cautery artefact:** coagulative homogenisation of margins; a cauterised margin that cannot be assessed must be reported as "cannot assess", not negative.
- **Fixation window:** 10% neutral buffered formalin at about ten times tissue volume, penetration roughly one millimetre per hour; breast and HER2 testing demand six to seventy-two hours per ASCO/CAP rules — shorter or longer invalidates receptor results.
- **Pigments worth naming:** brown granular formalin pigment in blood-rich tissue fixed in acidic formalin (cleared by brief alkali treatment), Bouin's yellow pigment, and mercury pigment from B5 fixative removed by iodine then sodium thiosulphate.
- **Microtomy faults:** chatter from hard or over-decalcified tissue and dull blades; folds and wrinkles from a warm water bath; thick sections that blur nuclei and inflate apparent pleomorphism.
- **Floaters and carry-over:** stray tissue fragments from a dirty bath or forceps constitute another patient's tissue on your slide — a medico-legal event; the defence is bath hygiene, one-block discipline and comparison with the preceding case.
- **Downstream damage:** hydrochloric or nitric acid decalcification hydrolyses DNA — EDTA preserves it; parched biopsies left dry on gauze yield uninterpretable autolysis, a common failure in busy Indian outpatient endoscopy suites.

## A case where the artefact nearly made the diagnosis

A gastric antral biopsy from a forty-year-old is reported elsewhere as "suspicious for signet-ring carcinoma". On review, the "signet rings" are pale vacuolated cells crushed by forceps and under-fixed for barely two hours — nuclei are smudged, mucus is pooled, and the lamina propria is homogenised. Repeat biopsies, gently handled and fixed overnight in adequate formalin, show ordinary chronic gastritis. Nothing about the patient changed; only the pre-analytical handling did. Contrast a breast core with HER2 immunohistochemistry scored 2+ that fails at reflex in-situ hybridisation because fixation was three hours: per ASCO/CAP the assay is uninterpretable, and testing must be repeated on the excision specimen with proper fixation. Both cases teach the same lesson — before reading any slide, judge whether the tissue was worthy of the stain.

## Where candidates slip

Three slips recur. Crush artefact is read as "anisokaryosis" or "poorly differentiated carcinoma" — degenerate smudged cells cannot be graded, and the correct act is a repeat biopsy, not an adjective. Formalin pigment is called haemosiderin; the discriminator is Perls' Prussian blue, which stains haemosiderin blue and leaves formalin pigment unstained — a one-stain answer examiners love. And floaters are treated as a curiosity rather than an incident: a single benign prostate acinus on a negative bladder biopsy can trigger an unnecessary cystectomy conversation, so floaters must be flagged in the report and traced to the preceding block in the cutting order.

## Frequently asked questions

### Which artefact most closely mimics signet-ring carcinoma?

Crush and degenerative vacuolation of epithelial cells; nuclear smudging and pooling of mucus with poor fixation are the clues.

### What fixation is mandated for valid HER2 testing?

Ten percent neutral buffered formalin for six to seventy-two hours, per ASCO/CAP guidance.

### How is formalin pigment distinguished from haemosiderin?

Perls' Prussian blue stains haemosiderin blue; formalin pigment stays unstained and can be removed with brief alkali treatment.

### Which decalcifying fluid preserves FISH and molecular results?

EDTA — strong mineral acids destroy nucleic acids and fluorescence signals.

### What is a floater and why is it medico-legally serious?

A tissue fragment carried over from another case onto the slide; it can plant a false diagnosis and must be reported and audited.