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Mastoid Anatomy and Mastoidectomy Surgery

Basic to Clinical - A Comprehensive Guide

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PART 1: MASTOID ANATOMY - FROM BASIC TO CLINICAL

1.1 Mastoid Bone - Overview

• Squamous - forms the lateral skull wall
• Petrous - contains inner ear structures
• Mastoid - houses air cells
• Tympanic - forms the bony ear canal
• Styloid - attachment for ligaments/muscles

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1.2 Pneumatization of the Mastoid

"The mastoid also extends posteriorly into the occipital bone and communicates with medial cell tracts. Although the vestibular portion of the inner ear forms the medial wall of the antrum, the Koerner septum - the embryologic junction between petrosal and squamosal portions of the temporal bone - forms the lateral limit."

• Cummings Otolaryngology Head and Neck Surgery

• Early otologic history
• Middle ear ventilation
• History of otitis media
• Heredity

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1.3 Key Surgical Landmarks of the Mastoid

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1.4 The Facial Nerve in the Mastoid - Critical Anatomy

"The tympanic segment is the most common site of congenital dehiscence of the bony canal, especially above the oval window... Bony dehiscence by cholesteatoma is also common proximal to the second genu."

• Cummings Otolaryngology

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1.5 Trautmann's Triangle

• Anteriorly: The posterior semicircular canal
• Posteriorly: The sigmoid sinus
• Superiorly: The superior petrosal sinus/dura

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PART 2: MASTOIDECTOMY - TYPES, INDICATIONS, AND TECHNIQUE

2.1 What is Mastoidectomy?

1. Eradicating disease
2. Creating a safe, dry ear
3. Restoring/preserving hearing

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2.2 Indications

• Acute coalescent mastoiditis with subperiosteal abscess (emergency)
• Chronic suppurative otitis media (CSOM) with cholesteatoma
• Cholesteatoma (most common elective indication)
• Access route for cochlear implantation (facial recess approach)
• Access for acoustic neuroma (translabyrinthine approach)
• Chronic otitis media with intracranial complications (meningitis, lateral sinus thrombosis, epidural/subdural abscess, cerebral abscess, petrositis)
• Temporal bone malignancy (temporal bone resection)

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2.3 Nomenclature - Types of Mastoidectomy

"The nomenclature for mastoid surgery is often confusing and may describe a variety of approaches and techniques."

• Cummings Otolaryngology

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2.4 Surgical Steps - Canal Wall-Up Mastoidectomy

• Continuous intraoperative facial nerve monitoring (mandatory)
• Preoperative audiogram
• CT temporal bone to delineate anatomy and disease extent

• Shave 1-2 cm of hair around the ear
• Inject 5-10 mL of 1% lidocaine with 1:100,000 epinephrine postauricularly and in the EAC
• C-shaped postauricular incision placed ~1 cm behind the postauricular crease (Fig. 143.3)
• Incision carried down to temporalis fascia superiorly; to anterolateral mastoid tip inferiorly
• Two periosteal incisions: one along the temporal line, one perpendicular extending to mastoid tip
• Periosteum elevated and retracted forward with the auricle

• Mastoid cortex fully exposed
• Identify surface landmarks: temporal line, spine of Henle, posterior EAC wall

• First burr cut: along the temporal line (approximates level of middle cranial fossa floor / tegmen)
• Second burr cut: perpendicular to first, tangential to external bony canal, carried inferiorly to mastoid tip
• Larger burrs (cutting/fluted) used for cortical bone
• Diamond burrs used when approaching facial nerve or sigmoid sinus
• Continuous saline irrigation to clear bone dust, prevent heat transfer

• Identify position of tegmen (superior) and sigmoid sinus (posterior)
• Exenterate mastoid air cells between these key structures
• Thin the external auditory canal; remove bone from the zygomatic root area

• Identify and open the mastoid antrum
• Identify the short process of the incus (fossa incudis) - key landmark
• Identify the dome of the lateral semicircular canal - most reliable deep landmark

• Identify and skeletonize the mastoid segment of the facial nerve (CN VII)
• Nerve runs vertically just anterior to the digastric ridge

• Open the facial recess - the triangle bounded by the facial nerve (posteriorly), chorda tympani (anteriorly), and incus buttress (superiorly)
• This gives access to the posterior middle ear without disturbing the canal wall
• Used for cochlear implant electrode insertion

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2.5 Canal Wall-Down Mastoidectomy - Additional Steps

• Thorough removal of ALL mastoid air cells
• Aggressive saucerization of the cortical edges of the mastoid and tip
• Complete removal of the superior and posterior canal walls
• Meatoplasty (widening of the external meatus for cavity access and maintenance)
• Tympanic membrane usually reconstructed to create pneumatized middle ear space

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2.6 CWU vs CWD - Clinical Decision-Making

• Only-hearing ear (single operation eradication preferred)
• Poor anesthetic risk patients
• Poor follow-up compliance
• Low-lying middle cranial fossa dura + anteriorly positioned sigmoid sinus (small mastoid - limits CWU exposure)
• Extensive disease found intraoperatively
• Poorly developed mastoid with sclerotic bone

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2.7 Modified Radical Mastoidectomy (Bondy Procedure)

• Specifically for disease limited to the epitympanum
• Portions of the adjacent superior or posterior canal wall removed to exteriorize the disease
• The uninvolved middle ear is NOT entered
• Cholesteatoma matrix on the lateral surface of the ossicular heads is maintained in place as a lining for the cavity
• Defects of the canal and tympanic membrane are not repaired (unlike retrograde mastoidectomy)
• Suitable for small attic cholesteatomas

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2.8 Radical Mastoidectomy

• Performed for extensive disease not amenable to less aggressive procedures
• All mastoid air cells removed + canal wall down
• Tympanic membrane sacrificed
• Lateral ossicular chain sacrificed (malleus head, incus)
• Eustachian tube obliterated
• Creates a large common cavity
• Hearing loss is significant and expected; no attempt at reconstruction

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PART 3: COMPLICATIONS OF MASTOIDECTOMY

Intraoperative Complications

Postoperative Complications

• Meningitis
• Epidural/subdural abscess
• Intraparenchymal (brain) abscess
• Lateral sinus thrombosis
• Petrous apicitis (Gradenigo's syndrome)

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PART 4: CLINICAL PEARLS - HIGH-YIELD SUMMARY

1. MacEwen's (Henle's) triangle - the suprameatal triangle on the posteromedial surface of the EAC - marks the position of the antrum on the surface (clinically useful to find the mastoid antrum).
2. "Safe" vs "unsafe" ear: Atticoantral disease (unsafe - associated with bone destruction and cholesteatoma) warrants mastoid surgery; tubotympanic disease (safe - only mucosal disease, no bone destruction) can usually be managed medically or with tympanoplasty alone.
3. Koerner's septum is a thin bony plate that is the embryologic fusion line between squamous and petrous temporal bone. It can falsely give the surgeon the impression of reaching the antrum - the true antrum lies medial to this.
4. Scutum (tympanic spine) - the lateral wall of the attic; its erosion on CT is an early sign of attic cholesteatoma.
5. Triad of danger: When drilling, always maintain awareness of the tegmen (superior), sigmoid sinus (posterior), and facial nerve (anterior-inferior) - these are the three structures that, if violated, can be catastrophic.
6. Citelli's angle (sinodural angle) - the angle between the sigmoid sinus and the dural plate. Citelli's abscess forms here in acute mastoiditis.
7. Canal wall-down cholesteatoma recidivism is 6-20% vs 25-45% in canal wall-up procedures - a major factor in choosing approach.
8. Second-look surgery after CWU at 9-12 months is standard to detect residual cholesteatoma, especially in children.
9. Facial recess = most important space in CWU mastoidectomy. Bounded by facial nerve, chorda tympani, and incus buttress. Opening it provides posterior middle ear access without removing the canal wall.
10. Cochlear implantation uses a modified CWU mastoidectomy with facial recess approach to insert the electrode array through the round window or cochleostomy.

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• Cummings Otolaryngology Head and Neck Surgery, Ch. 143 (Mastoidectomy) and Ch. 126 (Temporal Bone Anatomy)
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 2, Ch. 103 (Translabyrinthine/Cortical Mastoidectomy)
• StatPearls - Mastoidectomy (NCBI)
• Cleveland Clinic - Mastoidectomy