A 32-year-old woman presents to the gynaecology clinic with a 2-year history of heavy menstrual bleeding and lower abdominal pain. On examination, the uterus is enlarged, firm, and irregularly nodular. Transvaginal ultrasound reveals multiple well-defined hypoechoic lesions within the myometrium, the largest measuring 4 cm. Histopathology shows smooth muscle cells arranged in interlacing bundles with increased cellularity but no atypia or mitotic activity. Which cellular adaptation is most prominently demonstrated in this lesion?

Question

Accepted Answer

C. Hyperplasia of smooth muscle cells with benign proliferation. ## Diagnosis: Uterine Leiomyoma (Fibroid)

### Pathological Basis

**Key Point:** Uterine fibroids are benign smooth muscle tumours that demonstrate **hyperplasia** — an increase in the NUMBER of smooth muscle cells — rather than hypertrophy (increase in cell SIZE).

### Distinguishing Hyperplasia from Hypertrophy

| Feature | Hyperplasia | Hypertrophy |
|---------|-----------|----------|
| **Definition** | ↑ Number of cells | ↑ Size of individual cells |
| **Mechanism** | Increased mitotic activity (controlled) | Increased protein synthesis per cell |
| **Cell count** | Elevated | Normal |
| **Individual cell size** | Normal | Enlarged |
| **Reversibility** | Reversible if stimulus removed | Reversible if stimulus removed |
| **Example** | Leiomyoma, endometrial hyperplasia | Cardiac hypertrophy, skeletal muscle |

**High-Yield:** Leiomyomas show:
- Increased NUMBER of smooth muscle cells (hyperplasia)
- Normal mitotic rate (benign, not dysplastic)
- Absence of atypia or increased mitotic figures
- Well-demarcated, encapsulated lesions

### Clinical Pearl

The distinction matters: **hyperplasia = benign proliferation with normal cell morphology**, whereas dysplasia = abnormal morphology with increased mitotic rate and atypia (premalignant). This fibroid shows none of the latter features.

### Pathophysiology

Uterine fibroids arise from:
1. Monoclonal proliferation of a single smooth muscle cell (somatic mutation)
2. Altered response to oestrogen and progesterone
3. Abnormal growth factor signalling (TGF-β, FGF pathways)
4. Result: controlled but excessive hyperplasia

**Mnemonic: HyPERplasia = PERcentage of cells ↑**

![Cellular Adaptations — Hyperplasia, Hypertrophy diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/2791.webp)

Answer

A. Hypertrophy of smooth muscle cells in response to chronic irritation

Answer

B. Metaplasia of endometrial tissue to smooth muscle

Answer

D. Dysplasia progressing toward malignant transformation

Explanation

Diagnosis: Uterine Leiomyoma (Fibroid)

Pathological Basis

Distinguishing Hyperplasia from Hypertrophy

Clinical Pearl

Pathophysiology

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Feature	Hyperplasia	Hypertrophy
Definition	↑ Number of cells	↑ Size of individual cells
Mechanism	Increased mitotic activity (controlled)	Increased protein synthesis per cell
Cell count	Elevated	Normal
Individual cell size	Normal	Enlarged
Reversibility	Reversible if stimulus removed	Reversible if stimulus removed
Example	Leiomyoma, endometrial hyperplasia	Cardiac hypertrophy, skeletal muscle