Before operating on the petrous bone, the surgeon should have mastered the three dimensional anatomy of the temporal bone. In this chapter, the anatomy encountered during surgery is demonstrated from a middle fossa, mastoid, and posterior fossa approach.
Step 2. Note anatomy of semicircular canals (Fig. 13.3)
Illustrated Steps with Commentary
Fig. 13.1 (Step 1) Anatomy of the middle cranial base.An anterior petrosectomy has been performed. The greater superficial petrosal nerve runs above the carotid artery. The hard bony capsule of the cochlea is medial to the genu of the carotid artery. The fundus of the internal auditory canal is wedged between the cochlea and the superior semicircular canal. The posterior fossa dura along the petrous face is exposed. (AE, arcuate eminence; (C6, C6 portion of the internal carotid artery; Co, cochlea; DPN, deep petrosal nerve; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 13.2 Magnified view of the fundus of the internal auditory canal exposed through the superior petrosa.Bill’s bar separates the superior vestibular from the facial nerve. The labyrinthine segment of the facial nerve passes from the internal auditory canal to the geniculate ganglion. The tympanic segment of the facial nerve passes posterior and the greater superficial petrosal nerve passes anterior from the geniculate ganglion. (AE, arcuate eminence; BB, Bill’s bar; Co, cochlea; FB, Fukushima’s bar [geniculate notch]; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)Fig. 13.3 (Step 2) Anatomical relationship of the semicircular canals and the middle ear.The bony capsules of the superior, posterior, and lateral semicircular canals have been dissected from mastoid air cells. The facial nerve passes between the middle ear and the lateral semicircular canal. The head of the malleus is seen articulating with the bony body of the incus. The tensor tympani articulates with the neck of the malleus. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.5 Schema of Fig. 13.4.(C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET, eustachian tube; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; IAN, inferior alveolar nerve; IPS, inferior petrosal sinus; LN, lingual nerve; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; MMA, middle meningeal artery; PSC, posterior semicircular canal; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve ; VI, abducens nerve; V-VII, vertical segment of the facial nerve)
Step 2. Note anatomy of the middle ear (Fig. 13.8)Step 3. Note cochlear aqueduct (Fig. 13.16)
Step 4. Blue line the semicircular canals (Fig. 13.17)
Illustrated Steps with Commentary
Fig. 13.6 (Step 1) Tympanic portion of the facial nerve.A superficial mastoidectomy has been performed. The body of the incus is seen in the atrium of the mastoid. The tympanic segment of the facial nerve is seen over the lateral semicircular canal. (I, incus; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve)Fig. 13.7 Facial recess.The bone over the genu of the facial nerve has been exposed anterior to the lateral semicircular canal by removing the lateral wall of the facial canal. The long crus of the incus, the stapes, and the promontory are seen through the facial recess framed by the short process of the incus, the chorda tympani, and the vertical portion of the facial nerve. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; LC (I), long crus of the incus; LSC, lateral semicircular canal; P, promontory; PSC, posterior semicircular canal; S, stapes; SM, stapedial muscle; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.8 (Step 2) Fibrocartilaginous ring.The articulation of the incus with the stapes, the chorda tympani, the tympanic membrane, and the fibrocartilaginous ring are seen. Care should be taken not to disrupt the fibrocartilaginous ring, which marks the circumference of the tympanic membrane. Disruption of the thin skin of the external auditory canal, the fibrocartilaginous ring, or the tympanic membrane contaminates the wound and serves as a conduit for cerebrospinal fluid to enter the external auditory canal. (CP, cochleariform process; CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; LC (I), long crus of the incus; LSC, lateral semicircular canal; M, malleus; Man (M), manibrium of the malleus; S, stapes; SC (I), short crus of the incus; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.9 The tympanic membrane.The tympanic membrane articulates circumferentially with the fibrocartilaginous ring and the manibrium of the malleus attaches to the tympanic membrane. The short crus of the incus is disarticulated from the epitympanic recess. The long crus articulates with the stapes. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; LC (I), long crus of the incus; LSC, lateral semicircular canal; M, malleus; Man (M), manibrium of the malleus; PSC, posterior semicircular canal; S, stapes; SC (I), short crus of the incus; SSC, superior semicircular canal; TM, tympanic membrane; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.10 Jacobson’s nerve on the promontory.The tympanic branch of the glossopharyngeal nerve (Jacobson’s nerve) courses along the promontory. This nerve provides sensory innervation to the mucous membrane of the middle ear. Its fibers are joined by sympathetic fibers to form the tympanic plexus. Fibers coalesce to form the lesser petrosal nerve, which exits through a small hole in the tegmen tympani lateral to the greater superficial petrosal nerve. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; LC (I), long crus of the incus; LSC, lateral semicircular canal; M, malleus; P, promontory; R, round window; S,stapes; SC (I), short crus of the incus; TN, tympanic nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.11 Enlarged view of Jacobson’s nerve, Fig. 13.10.(CT, chorda tympani; LC (I), long crus of the incus; P, promontory; R, round window; S,stapes; TN, tympanic nerve)Fig. 13.12 Jacobson’s nerve.Jacobson’s nerve emerges from the glossopharyngeal nerve into the infralabyrinthine and suprajugular spaces. (C7, C7 portion of the internal carotid artery; CT, chorda tympani; IX, glossopharyngeal nerve; JB, jugular bulb; PSC, posterior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)Fig. 13.13 Jacobson’s nerve.Jacobson’s nerve runs between the internal carotid artery and the jugular bulb. (C7, C7 portion of the internal carotid artery; ExVII, extracranial portion of the facial nerve; IX, glossopharyngeal nerve; JB, jugular bulb; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)Fig. 13.14 The stapedial muscle.The tiny tendon of the stapedial muscle exists under the proximal vertical portion of the facial nerve, very close to the external genu of the facial nerve. The tendon attaches to the neck of the stapes. (CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; Man (M), manibrium of the malleus; PSC, posterior semicircular canal; SM, stapedial muscle; SSC, superior semicircular canal;,TM, tympanic membrane; V-VII, vertical segment of the facial nerve)Fig. 13.15 The stapedial muscle.The facial nerve is raised to show the stapedial muscle. (CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; S, stapes; SM, stapedial muscle; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)Fig. 13.16 (Step 3) The cochlear aqueduct.The cochlear aqueduct passes from the base of the cochlea close to the vestibule and communicates with the jugular foramen close to the exit of the glossopharyngeal nerve. Drilling in front of the superior aspect of this structure risks injury to the cochlea. Drilling close to the inferior end of the cochlear aqueduct risks injury of the glossopharyngeal nerve. The cochlear aqueduct divides the bone into an infralabyrinthine and a suprajugular triangle. The infralabyrinthine triangle is delineated by the cochlear aqueduct, posterior fossa dura, and posterior semicircular canal. Extension of the superior leg of the infralabyrinthine triangle leads to the basal turn of the cochlea. Drilling cranial to the superior line of this triangle can lead to cochlear injury. The suprajugular triangle is defined by the cochlear aqueduct, jugular bulb, and C7 vertical portion of the internal carotid artery. An extension of the inferior leg of the suprajugular triangle leads to the ninth nerve canal. Drilling caudal to the inferior leg of this triangle can lead to glossopharyngeal nerve injury. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; IB, incus buttress; ILT, infralabyrinthine triangle; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SJT, suprajugular triangle; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)Fig. 13.17 (Step 4) Blue line of the semicircular canals.The hard bone around the semicircular canals can be thinned under constant irrigation until the canals are seen through the thinned bone. This maneuver is performed during a middle fossa or presigmoid approach to maximize the size of the operative field. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)Fig. 13.18 Opening the bony labyrinth.The orientations of the three semicircular canals are demonstrated. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; VVII, vertical segment of the facial nerve)Fig. 13.19 The vestibular aqueduct.The vestibular aqueduct opens into the vestibule close to the opening of the common crus. The position of the posterior semicircular canal can be estimated by following the endolymphatic sac to the vestibular aqueduct. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V, vestibule; VA, vertebral artery; V-VII, vertical segment of the facial nerve)Fig. 13.20 Opening the internal auditory canal.The facial, the cochlear, and the superior and inferior vestibular nerves travel in the internal auditory canal. The superior and inferior nerves are elevated to show the underlying facial and the cochlear nerves, respectively. (C, cochlear nerve; CA, cochlear aqueduct; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; IV, inferior vestibular nerve; JB, jugular bulb; M-VII, meatal segment of the facial nerve; P, promontory; SS, sphenoid sinus; SV, superior vestibular nerve; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)Fig. 13.21 Opening the basal turn of the cochlea.The vestibule connects the semicircular canals with the cochlea. Drilling anterior to the posterior semicircular canal under the facial nerve exposes the vestibule and the basal turn of the cochlea. (bCo, basal turn of the cochlea; C, cochlear nerve; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; IV, inferior vestibular nerve; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.22 The oval and round windows.To show the relationship between the internal auditory canal and semicircular canals, the posterior semicircular canal and a part of the superior semicircular canal are drilled away. The oval window is the seat of the head of the stapes bone. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; PSC, posterior semicircular canal; R, round window; SS, sphenoid sinus; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)Fig. 13.23 The cochlear aqueduct.The focus is on the cochlear aqueduct, which connects the basal turn of the cochlea with the jugular foramen. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; PSC, posterior semicircular canal; R, round window; SS, sphenoid sinus; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)Fig. 13.24 The oval window.The dissector is inserted through the oval window. The tip of the dissector can be seen in the vestibule. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; R, round window; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)Fig. 13.25 The round window.The dissector is inserted through the round window. The tip of the dissector can be seen in the vestibule. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)Fig. 13.26 The cochleariform process.The cochleariform process serves as a pulley for the tensor tympani muscle. The malleus and the incus have been removed. (CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; LSC, lateral semicircular canal; M, malleus; P, promontory; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)Fig. 13.27 The vestibule.The vestibule is opened. A white or yellow dot (Mike’s dot) marks the superior division of the vestibular nerve, which exits to innervate the lateral and superior semicircular canals. (CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; M, malleus; P, promontory; R, round window; SSC, superior semicircular canal; V, vestibule; VVII, vertical segment of the facial nerve)Fig. 13.28 White or yellow dot in the vestibule.The superior vestibular nerve is seen as a skeletonized white or yellow point. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; CP, cochleariform process; M, malleus; SSC, superior semicircular canal; TN, tympanic nerve)Fig. 13.29 The basal turn of the cochlea and facial nerve.The vestibule opens into the basal turn of the cochlea anteriorly. Removing the roof of the vestibule opens the fundus of the internal auditory canal. The facial nerve is on the opposite side of Bill’s bar. The cochleariform process is a landmark of the geniculate ganglion of the facial nerve when the translabyrinthine approach is performed. (bCo, basal turn of the cochlea; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.30 The basal turn of the cochlea.The relationship between the fundus of the internal auditory canal and the basal turn of the cochlea is demonstrated. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; CP, cochleari-form process; GG, gasserian ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; TP, transverse process; T-VII, tympanic segment of the facial nerve)Fig. 13.31 The basal turn of the cochlea.The facial nerve has been translocated inferiorly to expose the length of the basal turn of the cochlea. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; CP, cochleariform process; M, malleus; Mo, modiolus; SSC, superior semicircular canal; TP, transverse process)Fig. 13.32 The internal carotid artery.The genu of the carotid artery between carotid segments C6 and C7 is located anterior to the cochlea. (bCo, basal turn of the cochlea; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; FR, fibrocartilaginous ring; JB, jugular bulb; M, malleus; Man (M), manibrium of the malleus; Mo, modiolus; SSC, superior semicircular canal; TM, tympanic membrane)Fig. 13.33 The auditory tube (eustachian tube).The eustachian tube is lateral to the C6 segment of the carotid artery. (bCo, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; FR, fibrocartilaginous ring; JB, jugular bulb; M, malleus; Mo, modiolus; SSC, superior semicircular canal)Fig. 13.34 The auditory tube (eustachian tube).The facial nerve is returned to its normal position to demonstrate the relationship between the eustachian tube and the nerve. (C7, C7 portion of the internal carotid artery; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; M, malleus; MVII, meatal segment of the facial nerve; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)Fig. 13.35 Exposing the cochlea via the transmastoid approach.Drilling the posterior wall, the three turns of the cochlea are seen. (aCo, apical turn of the cochlea; bCo, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; JB, jugular bulb; M, malleus; mCo, middle turn of the cochlea; Mo, modiolus; SSC, superior semicircular canal; TC, transverse crest)Fig. 13.36 The relationship between the cochlea and the facial nerve.The facial nerve is returned to its normal position to demonstrate the relationship between the cochlea and the facial nerve. (aCo, apical turn of the cochlea; bCo, basal turn of the cochlea; CA, cochlear aqueduct; G, genu [second turn or external turn] of the facial nerve; M, malleus; Mo, modiolus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.37 The anatomy of the pars nervosa of the jugular foramen.The picture from chapter 16 (transjugular approach) demonstrates the ninth cranial nerve separated from the tenth and eleventh cranial nerves by the inferior petrosal sinus. The condyle has been opened to demonstrate the hypoglossal nerve and the jugular vein. The sigmoid sinus has been removed. (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; CT, chorda tympani; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; V-VII, vertical segment of the facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)Fig. 13.38 Schema of the intramastoid-1.Overview after the standard mastoidectomy. The facial nerve is skeletonized. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; PSC, posterior semicircular canal; R, round window; SPS, superior petrosal sinus; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)Fig. 13.39 Schema of the intramastoid-2.The mastoid portion of the facial nerve is seen overlying the cochlea. (Co, cochlea; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; TM, tympanic membrane; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 13.40 Schema of the intramastoid-3.A partial clivectomy is done after drilling of the semicircular canals and the cochlea. The inferior petrosal sinus is seen. The abducens nerve exists in the inferior petrosal sinus. The facial nerve has been posteriorly translocated. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; SPS, superior petrosal sinus; VI, abducens nerve; VII, facial nerve)Fig. 13.41 Schema of the intramastoid-4.After opening the dura, the abducens nerve is well seen. The nerve penetrates the clival dura and runs in the inferior petrosal sinus toward Dollero’s canal. (BA, basilar artery; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; SPS, superior petrosal sinus; VI, abducens nerve; VII, facial nerve)
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15 Combined Petrosal Approach
14 Transmastoid Approach: Retrolabyrinthine, Translabyrinthine, and Transcochlear Approaches
17 Total Petrosectomy with Partial Clivectomy
3 Transfacial Transmaxillary Approach
18 Anatomy for Posterior Skull Base Surgery
12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)
