Dysplasia

Definition

Disordered cellular development — proliferative, cytologically abnormal epithelium that has not breached the basement membrane. Often called atypical hyperplasia since it’s frequently preceded by metaplasia and hyperplasia. Occurs mainly in epithelium.

Cytologic features (7)

Increased epithelial layers · disorderly basal-to-surface arrangement · loss of basal polarity (nuclei away from basement membrane) · cellular/nuclear pleomorphism · increased nucleocytoplasmic ratio · nuclear hyperchromatism · increased mitoses.

Most common sites: uterine cervix, respiratory tract.

Natural history

Arises from chronic irritation/prolonged inflammation (same trigger class as metaplasia).

• Stimulus removed → may regress toward normal.
• Persists → may progress to carcinoma in situ (full-thickness atypia, basement membrane intact) → invasive cancer (membrane breached).

Genuinely bidirectional — this is why it needs follow-up, not just observation.

Dysplasia vs metaplasia

Clinical relevance

Basis of cervical/respiratory cancer screening — catching dysplasia before CIS or invasion. CIS vs invasive cancer = basement membrane intact vs breached — hence CIS/dysplasia is curable by local excision. Removing the underlying irritant (HPV, smoking, chronic inflammation) matters as much as excising the lesion.

Definition

Dysplasia means disordered cellular development. It describes an epithelium in which the normal, orderly process of cell maturation from the basal layer to the surface has broken down, producing cells that are proliferative and cytologically abnormal but have not yet breached the basement membrane. Because it is so often preceded or accompanied by metaplasia and hyperplasia, dysplasia is sometimes referred to as atypical hyperplasia. It occurs most often in epithelial tissue.

Cytologic Features

Epithelial dysplasia is recognised by a combination of architectural disorder and cellular atypia.

• Increased number of layers of epithelial cells.
• Disorderly arrangement of cells from the basal layer to the surface.
• Loss of basal polarity — nuclei lie away from the basement membrane rather than at their normal basal position.
• Cellular and nuclear pleomorphism.
• Increased nucleocytoplasmic ratio.
• Nuclear hyperchromatism.
• Increased mitotic activity.

The two sites where dysplastic change is most commonly encountered are the uterine cervix and the respiratory tract, both surfaces subject to sustained chronic irritation.

Etiology and Natural History

Dysplastic change typically develops in the setting of chronic irritation or prolonged inflammation — the same category of stimulus that produces metaplasia, and the two frequently coexist or evolve one into the other at the same site.

The course of dysplasia is genuinely variable, which is what makes it clinically significant rather than a fixed diagnosis.

• If the inciting stimulus is removed, dysplastic change may regress and the epithelium can return toward normal.
• In a proportion of cases, dysplasia instead progresses — first to carcinoma in situ, in which the cytologic abnormalities of dysplasia become full-thickness but remain confined above an intact basement membrane, and then potentially to invasive cancer once the basement membrane is breached.

Because either outcome is possible, dysplasia identified on biopsy is treated as a lesion requiring follow-up or intervention, not as a static finding to be noted and left alone.

Dysplasia Compared with Metaplasia

Dysplasia and metaplasia are easily confused because both are epithelial responses to chronic stimuli and both can occur at the same anatomical sites, but they differ in what actually happens to the cell.

Clinical Relevance

• Dysplasia is the histological substrate for cervical and respiratory cancer screening programmes — detecting it before it progresses to carcinoma in situ or invasive disease is the entire rationale for cervical cytology and bronchial surveillance in high-risk patients.
• The distinction between carcinoma in situ and invasive carcinoma rests entirely on the integrity of the basement membrane, which is why dysplastic and in situ lesions are managed as fully curable by local excision, unlike invasive disease with its risk of metastasis.
• Because dysplasia can regress when its cause is removed, identifying and treating the underlying chronic irritant — persistent HPV infection, ongoing smoking, chronic inflammation — is as important a part of management as excising the lesion itself.

Diagram 1: Normal Epithelium Compared with Dysplastic Epithelium

Draw two side-by-side cross-sections of stratified squamous epithelium sitting on a basement membrane (the cervix is the conventional example), normal on the left, dysplastic on the right.

Left — normal: an orderly stack of cell layers, small round nuclei confined to the basal third, cells becoming flatter and more mature toward the surface, uniform cell size throughout.

Right — dysplastic: a thicker stack of layers, nuclei of variable size and darkness scattered irregularly from base to surface rather than confined to the base, some enlarged and irregularly shaped nuclei, and a few mitotic figures drawn above the basal layer. The basement membrane beneath both sides must be drawn as a single, intact, unbroken line.

Labels required

• Label the basement membrane explicitly in both panels, and state that it remains intact on the dysplastic side — this is what separates dysplasia from invasive change.
• Individually label at least four of the seven cytologic features on the dysplastic side: increased layers, disordered arrangement, loss of polarity, pleomorphism, increased nucleocytoplasmic ratio, hyperchromatism, and abnormal mitoses — a single generic “atypia” label loses marks.
• Mark the location of mitotic figures specifically above the basal layer, since their presence in the upper layers (rather than confined to the base, as in normal epithelium) is itself a specific abnormal finding.

Errors commonly made

• Breaching the basement membrane in the dysplastic panel — this converts the drawing into invasive carcinoma and defeats the purpose of the comparison.
• Labelling the abnormal features as a single block (“dysplastic changes”) instead of naming each one, which is how examiners actually allocate marks on this diagram.
• Placing mitotic figures only in the basal layer of the dysplastic panel, missing the point that disordered mitotic activity through the full thickness is part of what defines dysplasia.

Diagram 2: Dysplasia to Carcinoma in Situ to Invasive Carcinoma

Draw three panels in sequence, each a cross-section of the same epithelium and basement membrane, showing increasing severity.

1. Mild-to-moderate dysplasia: atypical cells confined to the lower half to two-thirds of the epithelium, with more normal-appearing, maturing cells toward the surface.
2. Carcinoma in situ: atypical, disordered cells occupying the full thickness of the epithelium, with no normal maturation visible at the surface; basement membrane still intact and unbroken.
3. Invasive carcinoma: atypical cells breaking through the basement membrane and infiltrating into the underlying stroma as irregular nests and cords.

Labels required

• The basement membrane must be drawn and labelled in all three panels, marked “intact” in panels 1 and 2, and explicitly marked “breached” in panel 3.
• Panel 2 must be labelled with the point that full-thickness involvement, not just severity of atypia, is what defines carcinoma in situ.

Errors commonly made

• Drawing carcinoma in situ with a breached basement membrane, which contradicts its definition and makes it indistinguishable from invasive carcinoma.
• Failing to show a gradient of severity across the three panels, drawing panels 1 and 2 as identical and only changing the basement membrane in panel 3.