Histopathology

Histopathology, also termed Anatomical Pathology, entails the study of diseases on the structure or morphology of cells, tissues and body organs, both macro- and microscopically. Tissue samples are submitted to the pathology laboratory for the diagnosis of inflammatory disorders (which also include infectious or autoimmune diseases) as well as for the diagnosis of neoplasia (which includes benign and malignant tumours).

To submit a sample for histopathologic assessment, a patient is required to undergo a surgical procedure (which may include endoscopy) to obtain a sufficient sample.  This entails either a biopsy or an excision (resection) specimen, submitted to the laboratory in a fixative solution (usually formalin) and processed for examination.

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Common specimens received include skin, gastrointestinal, endometrial, prostate and breast biopsies, as well as lung, liver and kidney biopsies.

Excision specimens include the appendix, gallbladder, fallopian tubes or lymph nodes, while resection specimens (often in the management of a tumour) may comprise a breast lumpectomy or mastectomy, thyroidectomy, hysterectomy, colectomy, prostatectomy and nephrectomy.

The primary role of a histopathologic diagnosis is to provide specific information to the submitting clinician on the nature of the disease as well as the probable course (prognosis) thereof, to correctly guide patient management and treatment.  

Histopathology assists in the staging of tumours and the assessment of recurrence following therapy.

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Histopathologic assessment may also be the first step in the recognition of a particular genetic disorder and serves to drive further testing in this regard.  

Moreover, in the era of precision medicine and targeted chemotherapy, the histopathologist plays a crucial role with the oncology team in cancer treatment, with specialized immunohistochemical and molecular testing of the tissue samples.

In brief, histopathology specimens (i.e. tissue) are received at the laboratory in formalin solution, which fixes the sample and preserves the tissue in a life-like state.

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Upon receipt, the tissue is inspected and dissected by the attending pathologist (this is known as macroscopic examination or grossing).

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The dissected samples are placed in cassettes for automated processing overnight involving treatment with alcohol and xylene solutions, and finally impregnation with wax.

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The tissue embedded in wax is sectioned on a microtome by the histotechnology staff, with ultrathin sections mounted on a glass slide and stained with haematoxylin and eosin, to then be viewed by the histopathologist for diagnostic purposes.

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In standard cases, the turn-around-time (TAT) from specimen collection to diagnosis may range from 24 to 72 hours (this may be prolonged in complicated cases requiring supplementary histochemical and immunohistochemical staining).

Cytopathology entails a subdivision of histopathology which represents a screening and/or diagnostic investigation, most often of precancerous or cancerous lesions, by means of microscopic analysis of cellular material (as opposed to intact tissue, as for histopathology).

The most common specimen analyzed in the cytopathology laboratory is cervical cytology procured by scraping off cellular material from the uterine cervix using a brush or spatula.

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This specimen may be received in a fixative solution (so-called liquid-based cytology or LBC) or as an already prepared and fixed slide (so-called Pap smear).

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Other cytopathology specimens include various body fluids (e.g. those abnormally extruded into the abdominal or pleural cavity) and fine needle aspiration (FNA).

FNA refers to a procedure whereby cellular material is procured from any suspicious or abnormal lesions (usually nodules or tumours) for further microscopic examination.

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A thin needle is inserted into the lesion, usually through the skin and often under ultrasound or CT-scan guidance, making this procedure much less invasive than a formal tissue biopsy.

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Cytologic material received in fixative solutions at the laboratory may also readily be prepared for further analysis utilizing special and immunohistochemical stains, as well as numerous molecular pathology techniques (including human papillomavirus/HPV testing on cervical cytology specimens).