---
title: "Otosclerosis Part 1 - Causes, Pathogenesis, Types, Pathology"
description: "Comprehensive ENT notes on Otosclerosis - Definition, Causes, Pathogenesis, Types, Pathology - ideal for MBBS and ENT students."
source: "The ENT Resident"
canonical_url: "https://www.theentresident.com/ent-notes-lectures/otosclerosis-causes-types-pathogenesis"
categories: ["Otology"]
video: "https://www.youtube.com/watch?v=3hijxqu2fnk"
image: "https://media.theentresident.com/og-images/otosclerosis-causes-types-pathogenesis.png"
---

# Otosclerosis Part 1 - Causes, Pathogenesis, Types, Pathology

Comprehensive ENT notes on Otosclerosis - Definition, Causes, Pathogenesis, Types, Pathology - ideal for MBBS and ENT students. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=3hijxqu2fnk

## 🦴 Otosclerosis — Definition, Etiopathogenesis & Histopathology

Otosclerosis is a **high yield ENT topic**, especially for **vivas and MCQs**.

🚩 A **typical exam question** describes:

- A **middle aged female**
- **Progressive conductive hearing loss**
- Often worsens during **pregnancy**

This topic is covered as a **three part series**:
1. **Part 1:** Definition, etiopathogenesis & histopathology  
2. **Part 2:** Clinical features & investigations  
3. **Part 3:** Treatment  

---

### 🧠 What is Otosclerosis?

Otosclerosis is a **hereditary disorder of bone metabolism** involving the **otic capsule and chondral bone**, characterized by **abnormal bone remodeling**.

> What is the key pathology seen in Otosclerosis?

> What is the most commonly involved site in Otosclerosis?

---

### 📊 Epidemiology of Otosclerosis

- Affects **0.5–1%** of the population

- Onset: **20–30 years**

- Rare before **10 years** and after **40 years**

- **Female : Male = 2 : 1**

- Usually **bilateral** (≈85%)

- More common in:
  - Whites
  - Indians  

- Rare in:
  - Africans
  - Chinese & Japanese

> Why is Otosclerosis seen more commonly in middle aged females?

---

### 🧩 Types of Otosclerosis

Broadly classified into:

- Clinical otosclerosis
- Histological otosclerosis

#### 👂 A. Clinical Otosclerosis

Lesions cause **clinical symptoms** due to involvement of:
- Stapes
- Stapediovestibular joint
- Cochlea
- Round window

##### 🔹 Subtypes

1. Stapedial otosclerosis
2. Cochlear otosclerosis
3. Mixed otosclerosis

---

#### 1.  Stapedial Otosclerosis

- Most common type
- Causes **stapes fixation**
- Presents with **conductive hearing loss**
- Most common site - fissula ante fenestram

> What are the different sites of lesion in stapedial otosclerosis?

> What is Biscuit type of Otosclerosis?

> What is Circumferential type of Otosclerosis?

> What is Obliterative type of Otosclerosis?

#### 2. Cochlear Otosclerosis

- Lesions involve **cochlear endosteum**

- Rare compared to stapedial type

> Is there stapes involvement in Cochlear Otosclerosis?

> What type of hearing loss is seen in Cochlear Otosclerosis?

> What is Malignant Otosclerosis?

#### 3. Mixed Otosclerosis

- Involves **both stapes and cochlea**
- Causes **mixed hearing loss**

---

#### 🔬 B. Histological Otosclerosis

- Lesions present **histologically**

- **No clinical symptoms**
- Detected **post-mortem**
- Accounts for **9–12%** of cases

---

### 🧬 Etiology & Risk Factors of Otosclerosis

Exact cause unknown, but several factors implicated.

#### 🧬 Genetic Factors

- 50% familial, 50% sporadic

> What pattern of inheritance is seen in Otosclerosis?

> What are the genes involved in Otosclerosis?

#### 🦠 Viral Hypothesis

- Measles virus antigens found in active lesions
- Increased CD46 receptor expression
- Lower anti-measles IgG levels reported

> What are the Limitations of viral hypothesis for Otosclerosis?

#### 🧫 Autoimmune Factors

- Possible immune reaction against **type II collagen**

- Cytokines involved:
  - TGF-β1
  - Bone morphogenetic proteins (BMP)

#### 🧪 Hormonal Factors

- Worsening during **pregnancy**

- Progression during **menopause**

- Explains female predominance

#### 🧬 Syndromic Association (MCQ Alert 🚨)

Van der Hoeve Syndrome

> What is Van der Hoeve Syndrome? What is the triad seen in Van der Hoeve Syndrome?

---

### 🔄 Pathogenesis of Otosclerosis

Etiological factors act on:
- Otic capsule
- Labyrinthine capsule

#### 🧠 Key events in Otosclerosis

1. Enlargement of **perivascular spaces**
2. Bone resorption by osteoclasts
3. New bone deposition by osteoblasts
4. Neovascularization & vascular shunting
5. Thickened mucoperiosteum

➡️ Produces **Schwartz sign**.

> Describe the pathogenesis of Otosclerosis.

> What is Schwartz sign? What is it indicative of?

---

### 🧫 Gross Pathology of Otosclerosis

- Lesions appear:
  - Chalky white
  - Grey / yellow
  - Red (active lesions)

---

### 🔬 Histopathology of Otosclerosis

Two phases:
1. Early Spongiotic Phase
2. Late Sclerotic Phase

> What are the histopathological changes seen in the Early Spongiotic Phase of Otosclerosis?

> What are the histopathological changes seen in Late Sclerotic Phase of Otosclerosis?

### 🧪 Active vs Inactive Otosclerotic Lesions

#### 🔵 Active Otosclerotic Lesions

- Spongy bone
- Osteoclasts
- Dilated vessels
- Blue mantles of Manasse

> What are the Blue mantles of Manasse seen in Otosclerosis?

#### 🔴 Inactive Otosclerotic Lesions

- Dense compact bone
- Minimal vascularity
- Fibrous tissue predominance

---

### 📌 Key Exam Pearls

- Middle aged female + Conductive Hearing Loss → Think Otosclerosis
- Commonest site: **Fissula ante fenestram**
- Schwartz sign = **active lesion**
- Blue mantles of Manasse = **spongiotic phase**
- Van der Hoeve syndrome = MCQ favorite

---

📘 **Next Part:**  
[Clinical features, audiological findings & diagnosis of otosclerosis.](https://www.theentresident.com/ent-notes-lectures/otosclerosis-symptoms-signs-differential.md)

---

## About This Note

This note on Otosclerosis Part 1 - Causes, Pathogenesis, Types, Pathology is one of the free ENT study notes published by The ENT Resident. It is free to read on the website, and it is paired with a full video lecture on YouTube.

This note is categorized under [Otology](https://www.theentresident.com/ent-notes-lectures/category/otology.md). The category page lists all the free ENT notes on that topic.

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