The superior surface of petrosal part of temporal bone: Middle fossa surface of petrous part of temporal bone called tegmen. It contains vestibular and cochlear labrynth. It roofs carotid canal, EA canal, facial canal, & tympanic cavity. It has following surface landmarks: 1) Trigeminal impression:: on the upper surface of the petrous bone where Meckel’s cave and the semilunar ganglion sit. 2) GSP groove:Lateral to this impression is a small groove on the anterior, deep surface of the petrous portion of the temporal bone. The groove opens posteriorly into a canal, the hiatus of the facial canal. Grooves for the greater and lesser petrosal nerves: found on the upper surface of the petrous bone. Lateral to itrigeminal impression there are two small grooves, a medial sulcus of the greater petrosal nerve (sulcus n. petrosimajoris) and a lateral sulcus of the lesser petrosal nerve (sulcus n. petrosiminoris). They lead to two openings of the same name, a medial the greater petrosal opening (hiatus canalis n. petrosimajoris) and a lateral the lesser petrosal nerve opening (hiatus canalis n. petrosiminoris). 3) Arcuate eminence (SSC): Above and lateral to the hiatus is a bony prominence, the arcuate eminence, overlying the superior semicircular canal. The arcuate eminence (eminentiaarcuata) is lateral to these openings; it forms due to prominence of the vigorously developing labyrinth, particularly the superior semicircular canal. The internal auditory canal can be identified below the floor of the middle fossa by drilling along a line approximately 60 degrees medial to the arcuate eminence, near the middle portion of the angle between the greater petrosal nerve and arcuate eminence4) Tegmen tympani: A thin lamina of bone, the tegmen tympani, roofs the area above the middle ear and auditory ossicles on the anterolateral side of the arcuate eminence (between the petrosquamous fissure and the arcuate eminence).5) The carotid canal extends upward and medially and provides passage to the internal carotid artery and carotid sympathetic nerves in their course to the cavernous sinus6) Groove for superior petrosal sinus: The superior-most portion of the petrous portion of the temporal bone is a thin ridge, which constitutes part of the posterior border of the middle cranial fossa. This ridge contains the groove for the superior petrosal sinus.
Posterior fossa surface of petrous part of temporal bone blends with mastoid surface of temporal bone. It contains 1) IAM midway between apex and base of petrous. 2) Subarcuatefossafound posterior to EAM and is the site for penetration of subarcuate artery (branch of AICA) which supply SSC.3) vestibular aqueduct: Inferior lateral to EAC is opening for vestibular aqueduct that transmit enodlymphatic duct that communicate endolymphatic sac found between the dural layers and the endolymph of labrynth.4) Cochlear canaliculuswhere cochlear aqueduct (contain perilymph) opens. found at the antromedial edge of jugular foramen just superior and lateral to glossopharyngeal nerve where it enters the jugular foramen. During drilling of posterior lip of IAM care should be given to avoid injury of 1) Common crus of posterior and superior canals which found lateral to the entry of subarcuate artery. 2) Vestibule and Posterior semicircular canal: which are away from EAM by average 7mm 3) Vestibular aqueduct: the endolymphatic duct that marked by the endolymphatic ridge at the level of posterior canal. 4) Inferiorly: the high arched jugular bulb.
The course of the facial nerve can be roughly divided into 5 segments, 1) The pontine segment, between the brainstem and porus, measures 23 to 24 mm in length. At this point the facial nerve is anterior to the cochleovestibular nerve. The special sensory and visceral efferent components of the facial nerve pass in a separate bundle adjacent to the main motor trunk as the nervusintermedius.2) The meatal segment, within the internal auditory canal, is 7 to 8 mm in length. The facial nerve passes superior to the falciform crest in the lateral aspect of the canal and is separated from the superior vestibular nerve by a vertical crest of bone (Bill's bar).3) The labyrinthine segment, between the meatal segment and geniculate ganglion, is 4 mm in length. The osseous canal surrounding the facial nerve is narrowest at the most proximal portion of the labyrinthine segment. This segment passes anterolaterally, paralleling the axis of the arcuate eminence of the superior semicircular canal, and passes superior and in proximity to the basal turn of the cochlea. The geniculate ganglion is triangular and averages 1.09 mm in length. 4) The tympanic or horizontal segment, between the geniculate ganglion and second genu, is 12 to 13 mm in length. The proximal edge of the geniculate ganglion is 5 mm anterosuperior to the posterior edge of the processuscochleariformis. The facial nerve passes superior to the oval window niche, a region where in approximately 55% of cases it is dehisc 5) The mastoid or vertical segment, between the second genu and stylomastoid foramen, measures 15 to 20 mm in length. At the second genu, the semicircular canal lies 0.5 mm posterosuperior to the facial nerve. The digastric ridge is a useful landmark just posterior to the stylomastoid foramen. 6) Extratemporal segment (Stylomastoid foramen to pesanserinus): 15-20mm
Cholesteatoma eroding the horizontal semicircular canal, CT. A: Cholesteatomaopacifies the upper attic and antrum. Note the rounded, smooth margins. There is erosive scalloping of the bone covering the horizontal semicircular canal (arrow). The cholesteatoma has reached the lumen of the canal, causing a fistula. B: Normal right side shows the intact cortex with a normal thickness (arrow).
Glomusjugulare, axial CT. The lesion (white arrow) was visualized through the tympanic membrane. There is demineralization (black arrows) around the jugular foramen. The white cortical line is indistinct and poorly visualized. A small amount of demineralized bone (white arrowhead) on the posterior cortex of the carotid canal indicates tumor. Compare the demineralized bone with the intact cortex and bone on the opposite side.Glomusjugulare, MR T1-weighted image after intravenous contrast. The tumor (T) is visualized in the region of the jugular foramen. Its interface (arrow) with the posterior fossa is clearly defined. The bright signal (arrowhead) in the sigmoid sinus represents slow flow of blood with gadolinium. The margins of the lesion can be clearly seen, though the bony landmarks cannot.
High-resolution CT scan of a longitudinal skull fracture passing approximately parallel to the petrous ridge across the middle fossa floor and squamous portion of the temporal bone. Transverse fracture of the right temporal bone in the axial (A) and coronal (B) planes. Longitudinal fracture of the temporal bone follows the long axis of the petrous apex and crosses the floor of the middle cranial fossa near the foramen spinosum. The usual site of facial nerve injury is its labyrinthine segment. B: Transverse fracture of the temporal bone. The fracture line passes between the foramen magnum posteromedially and the foramen spinosum area anterolaterally and traverses the long axis of the petrous pyramid.
1) Epitympanum2) Middle ear bone articulation3) Body of incus4) Aditus of antrum5) Mastoid antrum6) LSC7) vestibule8) Tympanic segment of facial nerve 9) Pourusacousticus10) Internal auditory canal11) Midlle turn of cochlea 12) Petrous apex13) Head of malleus
Hugh D. Curtin, James D. Rabinov and Peter M. Som(2003): Central Skull Base: Embryology Anatomy, and Pathology in Central skull base in Head and Neck Imaging. Peter M. Som & Hugh D. Curt (edit) Mosby, Inc. St. Louis, Chapter 12 FOURTH EDITION. Volume one 785- 863
Superior surface of petrous bone Trigeminal depression Arcuate eminence
Medial surface of petrous bone Subarcuate fossa & AIAM Vestibular aqueductCochlear canaliculus Jugular foramen
References Hugh D. Curtin, James D. Rabinov and Peter M. Som(2003): Central Skull Base: Embryology Anatomy, andPathology in Central skull base in Head and NeckImaging. Peter M. Som & Hugh D. Curt (edit)Mosby, Inc. St. Louis, Chapter 12 FOURTH EDITION.Volume one 785- 863