What are the boundaries of a cortical mastoidectomy?

Boundaries of Cortical Mastoidectomy

Cortical mastoidectomy is bounded superiorly by the tegmen mastoideum and middle fossa dura, posteriorly by the sigmoid sinus, inferiorly by the mastoid tip, anteriorly by the posterior wall of the external auditory canal, medially by the antrum, and laterally by the mastoid cortex.

Anatomical Boundaries

The surgical limits of cortical mastoidectomy are defined by critical anatomical structures that must be identified and preserved:

Superior Boundary

• Tegmen mastoideum (middle fossa dura plate) forms the roof of the mastoid cavity 1
• This represents the floor of the middle cranial fossa and must not be violated to prevent CSF leak or intracranial complications 1
• In cases with a low-lying tegmen, special surgical considerations are required 2

Posterior Boundary

• Sigmoid sinus defines the posterior limit 1, 3
• The sinus must be identified and carefully preserved during drilling 3
• An anteriorly positioned or lateral sigmoid sinus may significantly limit the extent of mastoidectomy 2

Inferior Boundary

• Mastoid tip marks the inferior extent 4
• Dissection extends to the level of the digastric ridge 4

Anterior Boundary

• Posterior wall of the external auditory canal 2, 5
• The lateral attic wall (scutum) is the most anterior superior structure 2
• In cortical mastoidectomy, the canal wall is preserved (unlike in canal wall down procedures) 2

Medial Boundary

• Mastoid antrum represents the medial endpoint 5, 4
• The antrum connects to the epitympanic recess and middle ear 4
• Dissection proceeds until the antrum is widely opened 5

Lateral Boundary

• Mastoid cortex (outer cortical bone) 5, 4
• This is the starting point of the dissection, removed to access the mastoid air cells 4

Critical Structures to Identify

During cortical mastoidectomy, several landmarks must be identified to ensure complete disease removal while avoiding complications:

• Horizontal semicircular canal - serves as a key landmark medially 1
• Facial nerve (though not routinely exposed in simple cortical mastoidectomy, its course must be respected) 1, 3
• Zygomatic root cells anterosuperiorly (when present) 2

Common Pitfalls

• Inadequate superior dissection may leave disease in the epitympanic recess 2
• Failure to identify an anteriorly positioned sigmoid sinus can result in catastrophic hemorrhage 2
• Low-lying tegmen increases risk of dural injury if not recognized preoperatively on CT imaging 2
• Poorly developed zygomatic root cells may limit anterior exposure 2