RADIOLOGICAL ANATOMY OF TEMPORAL BONE

- Dr.N.SuriyaprakashJR , Dept of RadioDiagnosis.11/12/2017

Anatomy of temporal bone

Location

The temporal bone is situated on the sides and the base of the cranium and lateral to the temporal lobe of cerebrum.

PartsThe temporal bone consists of four parts

SquamousMastoidPetrousTympanic parts.

Mastoid process

The mastoid process is pyramidal bony projection located in the posterior portion of the temporal bone.

Styloid process

Slender pointed part of temporal bone. It projects inferiorly and anteriorly from the inferior surface of the temporal bone.

Zygomatic process

Borders / Sutures

Occipitomastoid suture separates occipital bone and mastoid

portion of temporal bone.

Squamosal suture separates parietal

bone and squamos portion of temporal bone.

Sphenosquamosal suture separates sphenoid bone and squamos portion

of temporal bone.

Zygomaticotemporal suture separates zygomatic bone and zygomatic

process of temporal bone.

External acoustic meatus

Cartilaginous lateral portion Funnel-shapedThe cartilaginous portion is continuous with the auricle, flexible and surrounded by fat.

Osseous medial portionSurrounded by the tympanic portion of the temporal boneTwo thirds of the length of the EAC Covered by skin and periosteumonly.

Middle Ear Cavity

Air space within the petrous portion of the temporal bone between the eustachian canal anteriorly and the mastoid air cells posteriorly

Laterally - TM Medially - Otic capsule and cochlear promontorySuperiorly- Tegmen tympani Inferiorly - Jugular floor

Subdivided into three spaceshypotympanummesotympanumepitympanum

Mastoid antrum is located in the anterosuperior part of the mastoid portion of the temporal bone and communicates with the epitympanum via a narrow channel termed the aditus ad antrum.

The antrum is surrounded by smaller variable-sized mastoid air cells

The mastoid air cells are divided by Koerner’s septum a thin bony structure formed by the petrosquamous suture that extends posteriorly from the epitympanum, into medial and lateral components.

Mastoid

Ossicles

Suspended by the TM, the ossicular ligaments to the epitympanicwalls, and the oval window.

The manubrium and lateral process of the malleus attach to the TM. The neck of the malleus is connected to the tensor tympani tendon .The circular head of the malleus articulates with the triangular body of the incus.

The short process of the incus projects posteriorly and is suspended within the epitympanic space, pointing toward the aditus ad antrum. The long process of the incus projects inferiorly, parallel to and behind the manubrium of the malleus. The tip of the long process bends medially to end in the lenticular process, which articulates with the head of the stapes

The stapes consists of the head, two crura, and a footplate . The footplate of the stapes attaches to the oval window of the vestibule and is secured by the annular ligament.

Inner Ear petrous portion of the temporal bone.

osseous labyrinth - consists of the cochlea, vestibule, and SCCs.

osseous labyrinth encapsulates the membranous labyrinth, which contains endolymph and is surrounded by perilymph.

Internal Auditory Canal

Bony conduit within the petrous portion of the temporal bone .

Transmits VII (facial) and VIII (vestibulocochlear) from the pontomedullary junction of the brainstem across the cerebellopontine angle (CPA) cistern to the inner ear .

The IACs should be nearly symmetric. Although there is wide variation in the exact shape and size of the canals, asymmetry of greater than 2 mm suggests pathology.

The IAC is partially divided by a transverse bony crest called the crista falciformis which runs parallel to the long axis of the canal and divides it into a superior and inferior portion.

A vertical crest termed Bill’s bar divides the superior component into anterior and posterior parts. The facial nerve is located in anterosuperior compartment, the cochlear nerve in the anteroinferior compartment, and the superior and inferior vestibular nerves in the posterosuperior and posteroinferior compartments, respectively

Carotid Canal

The carotid canal enters the base of the skull, ascends vertically, then turns horizontally and medially toward the petrous apex

This canal lies anterior and inferior to the cochlea and is separated from the middle ear cavity by a thin bony plate.

Jugular Foramen and Fossa

The jugular foramen is divided smaller anteromedial neural compartment (pars nervosa) containing cranial nerves IX, X, and XI larger posterolateral vascular compartment (the pars vascularis) containing the jugular vein.

The floor of the tympanic cavity normally forms the roof of the jugular fossa.

FACIAL NERVE

Facial nerve (VII cranial) consists of a motor and sensory root, the latter is also known as the nervous intermedius

NUCLEI OF ORIGIN Three brainstem nuclei contribute to the facial nerve: one motor, one secretomotor, and one sensory: Facial nerve nucleus in the pons as the motor fibres of the facial nerve loop posteriorly over the abducens nerve nucleus, they form the facial colliculus in the floor of fourth ventricle Superior salivary nucleus next to the facial nucleus supplies secretomotor parasympathetic fibres Nucleus of tractus solitaris lateral to the dorsal nucleus of the vagus nerve supplies taste fibres that eventually end up in the chorda tympani

COURSE Course of the facial nerve may be divided by the stylomastoid foramen into intracranial- intrapetrous part and extracranial part

INTRACRANIAL - INTRAPETROSAL PART Intracranial (cisternal) segment - zero branches

Meatal (canalicular) segment (internal auditory canal): 8 mm long, zero branches

Labyrinthine segment (IAC to geniculate ganglion): 3-4 mm long, 3 branches (from geniculate ganglion)

Tympanic segment (from geniculate ganglion to pyramidal eminence): 8-11 mm long, zero branches

Mastoid segment (from pyramidal eminence to stylomastoidforamen): 8-14 mm long, 3 branches

Intracranial (cisternal) segment

The nerve emerges immediately beneath the pons, lateral to the abducens nerve and medial to the vestibulocochlear nerve and is joined by the nervus intermedius, which has emerged lateral to the main trunk. Together the two travel laterally through the cerebellopontineangle to the internal acoustic meatus. The cisternal segment has no branches.

Meatal (canalicular) segment

Having been joined by the nervus intermedius,they are located in the anterior superior quadrant of the internal auditory canal, above the falciform crest and anterior to Bill's bar.

The meatal segment has no branches.

Labyrinthine segment

As the facial nerve and nervusintermedius pass through the anterior superior quadrant of the internal acoustic meatusit enters the Fallopian canal passing anterolaterally between and superior to the cochlea(anterior) and vestibule(posterior), and then bends posteriorly (the anterior or first genu) at the geniculateganglionwhere the nervusintermedius joins the facial nerve and where fibers for tte synapse .

three branches originate: greater superficial petrosal nerve lesser petrosal nerve external petrosal nerveshortest only measuring 3-4 mmnarrowest and the most susceptible to vascular compromise

Tympanic segment

As the nerve passes posteriorly from the geniculate ganglion it becomes the tympanic segment (8-11 mm in length) and is immediately beneath the lateral semicircular canal in the medial wall of the middle ear cavity.

The nerve passes posterior to the cochleariform process, tensor tympani and oval window Just distal to the pyramidal eminence the nerve makes a second turn (posterior or second genu) passing vertically downwards as the mastoid segment.

The tympanic segment has no branches.

Mastoid segment

Measures 8-14 mm in length

Extends from the posterior genuto the stylomastoid foramen

It runs in the medial wall of the aditus ad antrum of the mastoid.

It gives off three branches Nerve to stapedius Chorda tympani terminal branch of the nervus intermedius Nerve from the auricular branch of the vagus nerve (CN X)

Extra-temporal segmentAs the nerve exits the stylomastoid foramen, Sensory branch that supplies part of the external acoustic meatus and tympanic membrane. Muscular branches - Passes between the posterior belly of the digastric muscle and the stylohyoid muscle, supplying both and then enters the parotid gland. Lying between the deep and superficial lobes of the gland the nerve divides into two main branches at the pes anserinus -superior temporofacial and inferior cervicofacial branches. From the anterior border of the gland, five branches emerge Temporal Zygomatic BuccalMandibular (marginal) Cervical

N

The facial nerve is the only cranial nerve that may show normal post-contrast enhancement.

Typically enhancement is seen: Anterior genu (geniculate ganglion) Posterior genu (between tympanic and mastoid segments) Some enhancement can also be seen in the labrynthine, tympanic and mastoid segments. Proximal greater superfical petrosal nerve

No enhancement should be seen in:o Cisternal segment (that in the cerebellopontine angle)o Meatal segment (that in the internal acoustic meatus)o Extracranial segment (beyond the stylomastoid foramen)

TEMPORAL BONE IMAGING TECHNIQUESCT and MRI are currently the most widely used techniques for

imaging the temporal bone.

Each technique has advantages and disadvantages, and often more than one examination is necessary for a complete temporal bone evaluation.

CT Excellent for assessing the osseous structures of the temporal bone Not ideal for evaluating the soft tissue contents of the otic capsule, brain, or vessels.

MRI Characterizing the cerebrospinal fluid (CSF), brain, and cranial nerves.

AXIAL SECTIONS OF

TEMPORAL BONE

The carotid canal lies just anterior to the jugular fossa, forming a “snowman”-like configuration. Both demonstrate sharp cortical margins. Inferiorly only a small spine, the caroticojugular spine, separates the two as they converge to enter the carotid sheath. The descending facial nerve canal is lateral to the jugular foramen, seen as a rounded well-corticated lucency. The mandibular condyle and TMJ can also be seen.

Jugular foramen level.

EAC - Anterior and posterior walls of the bony demonstrate dense, sharp cortical margins without soft tissue covering. The anterior margin of the EAC forms the posterior lip of the TMJ.

Cochlear aqueduct - Medial funnel-shaped opening seen as a triangular lucency facing the CPA, progressively enlarging from lateral to medial. The opening of the aqueduct may be large and mimic the IAC.

The descending facial nerve canal is easily identified posterior to the EAC.

The petrooccipital fissure separates the temporal bone from the occiput.

Inferior tympanic level

The carotid canal can be seen early in its anteromedial course through the skull base, parallel and medial to the tensor tympani muscle at this level.

The tensor tympani muscle is lateral and parallel to the carotid canal

The normally thin TM may be visible.

The descending facial nerve canal can be seen just posterior to the pyramidal eminence.

The vestibular aqueduct is seen as a thin bony lucency along the posterior margin of the temporal bone, near its opening to the posterior cranial fossa.

Midtympanic level

The manubrium of the malleus parallels the TM.The manubrium of the malleus lies parallel and anterior to the long process of the incus.

Along the posterior wall of the middle ear is the pyramidal eminence, with the facial nerve recess lateral and the sinus tympani medial to the eminence.

The descending facial nerve canal can be seen just posterior to the pyramidal eminence.

Facial nerve recess

Sinus tympaniDescending

VII nerve canal

The stapedial superstructure (head, crura, and tympanic portion of the footplate) is often seen, forming an arch over the oval window.

The stapes suprastructure is medial to the incus

The apical, middle, and basal cochlear turns are seen at this level along with the round window niche at the basal turn.

The crura of the stapes can be seen extending toward the oval window

Tensor tympani tendon can be seen making a 90-degree turn and attaching to the neck of the malleus.

Epitympanic–internal auditory canal level

Round head of the malleus and the triangular body and short process of the incusare seen in their characteristic “ice cream cone” configuration.

The IAC is slightly funnel-shaped and ends in an ovoid fundus.

The canals for the facial nerve, cochlear nerve, superior vestibular nerve, and inferior vestibular nerve (singular canal) can be seen leaving the fundus of the IAC.

Tympanic segment is seen coursing along the medial wall of the tympanic cavity

The modiolus and interscalarseptae of the cochlea are visualized posterolateral to the cochlea.

The lateral SCC is seen protruding into the middle ear.

The labyrinthine segment of the facial nerve canal (fallopian canal) can be seen extending to the anterior genu, and the tympanic segment is seen coursing along the medial wall of the tympanic cavity.

The aditus and antrum is situated between the epitympanum and mastoid antrum. The mastoid antrum lies posterior and lateral to the aditus ad antrum and opens into many mastoid air cells. The posterior SCC and common crus of the posterior and superior SCCs can be seen. More superiorly the superior SCC is present.

Mastoid antrum level

CORONAL SECTIONSOF

TEMPORAL BONE

Coronal temporomandibular joint level

The horizontal carotid canal is seen as an oval structure just lateral to petrooccipital suture.

The semicanal for the tensor tympani muscle is seen as a small lucency lateral to the carotid canal.

The air-filled eustachian tube is inferior to the tensor tympani, and the TMJ is seen laterally

Tensor tympani muscle is seen along the medial wall of the middle ear, with the cochleariform process separating it from the eustachian tube below. The anteriormost part of the cochlea is medial to the tensor tympani. The geniculate ganglion is seen as a small lucency superior to the cochlea

Geniculate ganglion level

Superior and inferior walls of the EAC are seen well.

The TM may be identified as a thin filamentous structure extending from the scutum superiorly and coursing parallel to the plane of the long process of the malleus to attach to the limbus inferiorly.

The head and neck of the malleus can be seen in the epitympanic space, with the tendon of the tensor tympani muscle attaching to neck.

The basal and second turn of the cochlea are visualized.

The labyrinthine and tympanic segments of the facial nerve are seen as two lucencies superior to the cochlea.

Anterior tympanic level

This level shows the long process and lenticular process of the incus and the incudostapedial articulation as an L-shaped configuration.

Prussak’s space is seen between the incus and scutum. The tympanic segment of the facial nerve canal is seen along the medial wall of the middle ear just superior and lateral to the cochlea.

Midtympanic level

Prussak’s space

The full extent of the IAC is well visualized at this level, with the central crista falciformis dividing the canal into two portions.

Oval window is seen as a bony defect in the lateral portion of the vestibule.

Beneath the lateral SCC, the horizontal portion of the facial nerve canal appears as a small circular structure.

The epitympanic space lies just lateral to the lateral SCC.

Oval window level

Posterior tympanic level

The facial nerve recess is lateral to and the sinus tympani medial to the pyramidal eminence.

The round window niche is seen along the basal turn of the cochlea.

The jugular foramen – dome shaped outline.

The mastoid segment of the facial nerve canal can be identified lateral to the jugular foramen, running nearly vertical and extending toward the stylomastoidforamen.

The mastoid antrum is seen superiorly and laterally.

Portions of the lateral and superior SCCs can be seen.

Jugular foramen level

SPECIAL VIEWS

Stenvers’ view

Stenvers’ view MIDSUPERIOR SCC LEVEL. The superior SCC is seen in cross

section.

Stenvers’ view COMMON CRUS LEVEL. In addition to common crus, portions of the posterior SCC and superior SCC are seen.

Oblique coronal projection. Superior anatomic detail. Used to assess electrode placement following the insertion of a cochlear implant.

Stenvers’ view COCHLEA LEVEL. The turns of the cochlea are seen, as is the round window and descending facial

nerve canal .

Stenvers’ view INCUDOMALLEOLAR JOINT LEVEL. The incudomalleolarjoint is well seen between body of incus (I) and head of malleus (M).

Pöschl’s view The plane of projection is perpendicular to the long axis of the temporal bone. Projection the temporal bone is imaged from its anteromedial to posterolateral aspects.

The superior SCC is seen as a ring, and the posterior SCC is seen in cross section. The tympanic segment of the facial nerve

canal is seen in cross section.

PÖSCHL’S VIEW MIDSUPERIOR SCC LEVEL

The modiolus (m) is seen along its axis

PÖSCHL’S VIEW MODIOLUS LEVEL

EAC ATRESIA

COCHLEAR ANOMALIES (CLASSIFICATION) Have different presentation depending on the timing of developmental arrest.Divides congenital cochlear anomalies according to the timing of the developmental arrest.

Complete labyrinthine aplasia or Michel deformity: 3rd weekCochlear aplasia : 4th weekCommon cavity malformation to the cochlea and vestibule: early 5th weekCochlear incomplete partition type including Cystic cochleovestibular anomaly: late 5th weekCochlear hypoplasia: 6th weekCochlear incomplete partition type II including mondinidysplasia: 7th week

Complete labyrinthine aplasia Congenital abnormality of the inner ear and is characterised by bilateral absence of differentiated inner ear structures with resultant anacusis.

MICHEL APLASIA,

INCOMPLETE PARTITION - I(CYSTIC COCHLEOVESTIBULAR MALFORMATION)

Abnormal cochleaOnly 1.5 turns (instead of the normal 2.5 turns)Normal basal turn with a cystic apex in place of the distal 1.5 turns

Enlarged vestibule with normal semicircular canalsEnlarged vestibular aqueduct containing a dilated endolymphaticsac

MONDINI MALFORMATIONincomplete partition type II anomaly with large vestibular aqueduct.

Thank You . . .