Tympanoplasty Part 1 - Definition, Types, Grafts, Indications, Contraindications

Tympanoplasty: Part 1 - Definition, Types, Grafts, Indications, Contraindications

Tympanoplasty is a vast topic, so we'll break it down into two parts.

In this first part, we'll cover:

• Definitions (Myringoplasty vs. Tympanoplasty)
• Brief overview of middle ear physiology and the effect of TM perforation
• Types of Tympanoplasty (Wullstein's Classification)
• Different Graft Materials used
• Indications and Contraindications
• Principles of Hearing Restoration
• Prerequisites for TM repair
• Goals of Tympanoplasty
• Pre-operative Evaluation of patients

✨ Definitions

• Myringoplasty: An operation to repair a Tympanic Membrane (TM) perforation WITHOUT inspection of the ossicular chain.

It solely focuses on grafting the TM defect.

(Often wrongly referred to as Type 1 Tympanoplasty).

• Tympanoplasty: A broader operation involving eradicating disease in the middle ear and reconstructing the hearing mechanism, with or without TM grafting. This procedure definitely involves inspecting the ossicular chain and performing ossicular reconstruction if needed.

✨Key Difference: Myringoplasty is only TM repair without ossicular chain assessment. Tympanoplasty involves middle ear disease management, ossicular chain assessment/reconstruction, and TM grafting.

👂 Physiology of the Middle Ear and Effect of TM Perforation

Understanding how the middle ear works helps explain why TM perforations cause hearing loss and what tympanoplasty aims to fix.

• Impedance Matching / Transformer Action: The middle ear's primary function is to efficiently transfer sound energy from the air (low impedance) to the fluid-filled cochlea (high impedance).

This is achieved mainly through:

1. Lever Action of Ossicles: The lever arm ratio between the malleus handle and incus long process (approx. 1.3:1) provides a mechanical advantage.

2. Hydraulic Action of the Tympanic Membrane: The effective vibratory area of the TM is significantly larger than the area of the stapes footplate at the oval window. The average areal ratio is about 14:1 (considering only the effective 2/3 of TM).

   • Combined Effect: The product of these two actions (~18:1 to 22:1) creates a substantial pressure increase at the oval window.

• Role of the Round Window:

The round window acts as a relief opening for the incompressible cochlear fluid to move freely in response to the stapes footplate's piston-like motion.

In a normal ear, the intact TM protects the round window from direct sound pressure, ensuring a phase difference between the oval and round windows (sound reaches the oval window first via the ossicular chain, causing the round window membrane to bulge outwards, and vice-versa).

• Effect of TM Perforation:

  • Disrupts the impedance matching mechanism (loss of hydraulic action).

  • Sound waves reach both the oval window (via ossicular chain) and the round window simultaneously (no phase difference). This results in the sound-induced movements of perilymph largely cancelling each other out, leading to hearing loss.

🏥 Types of Tympanoplasty (Wullstein's Classification, 1956)

This classification describes different scenarios based on the TM and ossicular chain defect, and where the graft is placed relative to the stapes footplate (or remaining ossicles):

• Type 1:

  • Defect: TM perforation only. Ossicular chain is intact.
  • Procedure: Graft is placed on the malleus handle or on the remnant TM to close the perforation. Equivalent to Myringoplasty.

• Type 2:

  • Defect: TM perforation with erosion of the malleus (usually the handle).
  • Procedure: Graft is placed on the incus or on the remaining malleus remnant to contact the ossicular chain.

• Type 3:

  • Defect: TM perforation with absence/erosion of both malleus and incus. Only the stapes suprastructure is intact.
  • Procedure: Graft is placed directly on the stapes suprastructure. The new TM covers the stapes head.

What is Collumela Tympanoplasty?

• Type 4:

  • Defect: TM perforation with absence/erosion of malleus and incus. Only the stapes footplate is present (suprastructure is gone).
  • Procedure: Graft is placed to cover the round window, creating a small air cavity ("Cavum minor") around it. Sound then acts directly on the stapes footplate at the oval window, while the round window is shielded.

• Type 5:

  • Defect: TM perforation with absence/erosion of malleus and incus. Stapes footplate is fixed (e.g., due to otosclerosis). Round window is functioning.
  • Procedure: A new window (fenestra) is created in the lateral semicircular canal, and the graft is placed over this fenestra.

What is the other name of Type 5 Tympanoplasty?

🧬 Graft Materials Used

Various tissues can be used to repair the TM perforation:

• Temporalis Fascia

Why is Temporalis Fascia the most commonly used graft?

• Perichondrium

• Cartilage

What are the sites of harvesting Perichondrium and cartilage as grafts for Tympanoplasty?

What are the Indications of cartilage graft in Tympanoplasty?

• Areolar Tissue

• Other Options: Vein, Periosteum, Subcutaneous tissue, Fat, Fascia lata, Alloderm

What is Alloderm?

🏥 Indications for Tympanoplasty

• TM Perforation
• Hearing Loss
• Retraction Pockets / Atelectasis
• Cholesteatoma Surgery
• Tympanosclerosis

⛔ Contraindications for Tympanoplasty

Some contraindications are:

• Absolute Contraindications:

  • Very poor general health
  • Malignant tumors of external or middle ear.
  • Uncontrolled Cholesteatoma

• Relative Contraindications:

  • Active ear infection
  • Non-functioning Eustachian Tube

📘 In my detailed notes, I’ve discussed an exhaustive list of Absolute and Relative Contraindications of Tympanoplasty.

🎯 Principles of Hearing Restoration (What surgery aims to achieve):

1. Intact TM
2. Intact Ossicular Chain
3. Two Functioning Windows
4. Acoustic Separation of Windows
5. Functioning Eustachian Tube
6. Functioning Sensorineural Apparatus

🎯 Prerequisites for Myringoplasty:

• Ear should be dry (ideally for ~3 months)
• Eustachian tube should be patent
• No focus of infection in nose, paranasal sinuses, nasopharynx
• Good cochlear function
• Healthy middle ear mucosa

🎯 Goals of Tympanoplasty:

1. To achieve a dry ear by eradicating middle ear disease (maintaining a safe ear).
2. To restore or improve hearing by closure of the TM perforation (grafting) and/or ossicular chain reconstruction.

🩺 Pre-operative Evaluation of patient for Tympanoplasty

• Complete History and Head & Neck Examination

• Otoscopic Examination & Tuning Fork Tests

• Examination Under Microscope (EUM)

What is the focal length of microscopes used in Surgeries of Ear, Nose, Larynx?

• Pure Tone Audiometry (PTA) & Speech Discrimination Score (SDS)

What is the purpose of Pure Tone Audiometry in Tympanoplasty?

• Imaging:

  • High Resolution Computed Tomography (HRCT) of Temporal Bone
  • MRI Temporal Bone

Why do we need CT Scan and MRI of Temporal Bone in Tympanoplasty?