Anatomy of temporal bone

detailed anatomical description of temporal bone and its contents referenced from shambaugh and scott-brown

1. ANATOMY OF TEMPORAL BONE MODERATOR – DR. S N MUKHERJEE PRESENTER - DR. PRANEETH

2. INTRODUCTION Temporal bone is a composite structure consisting of tympanic bone, mastoid process, squama and petrosa . Styloid process eventhough is closely associated with temporal bone, is not considered as a part of it. From lateral view……, tympanic, squamous and mastoid portions are seen. All these parts are interfaced at their junctions forming tympano -squamous suture, tympano - mastoid suture and squamo -mastoid suture.

3. Tympanic bone Tympanic bone forms anterior, inferior and parts of posterior wall of EAC. I t constitutes posterior wall of glenoid fossa for TMJ. Tympano -mastoid suture is traversed by arnold’s nerve. Chorda tympani, anterior process of malleus and anterior tympanic artery traverse the petro-tympanic fissure. Henle’s spine is a projection at postero -superior aspect of external auditory canal.

4. Tympanic bone cont …. Inferiorly, the vaginal process, a projection of tympanic bone, forms the sheath of the styloid bone. Laterally, tympanic bone borders the cartilaginous EAC and medially it bears a circular groove called annular sulcus. Annular sulcus houses the annulus of TM except superiorly, where it is deficient called as notch of rivinus where t ympanic membrane attaches directly to the squama . Tympano -squamous and tympano -mastoid sutures are landmarks for the vascular strip incisions used in tympanomastoid surgery.

5. Squamous bone Squamous portion of temporal bone forms lateral wall of middle cranial fossa and interfaces with parietal bone superiorly, with zygomatic & sphenoid anteriorly. Medial surface is grooved by a sulcus for middle meningeal artery and lateral surface for middle temporal artery .

6. Mastoid bone Mastoid portion of temporal bone is the inferiorly extending projection seen on lateral surface. It is composed of squamous portion laterally and petrous portion medially separated by petrosquamous korner’s septum. Macewen’s triangle (fossa mastoidea ) – linea temporalis, posterosuperior margin of EAC and a tangent to posterior margin of EAC . It is a cribrose area having numerous, perforating small blood vessels. It laterally overlies the mastoid antrum .

7. Mastoid bone cont …. Mastoid foramen, located posteriorly on the mastoid process, is traversed by a mastoid emissary vein and 1 or 2 mastoid arteries. Inferiorly, sternocleidomastoid attaches to mastoid tip. Mastoid tip is easily palpable & is landmark for positioning of postauricular incisions. Linea temporalis is an avascular plane due to which it is an ideal location for the superior limb of ‘T’ musculoperiosteal incision used in the postauricular approach to the tympanomastoid compartment.

8. Mastoid bone cont …. Mastoid process in children is not fully developed, thus cannot be palpated easily. Hence, postauricular incision in children should be given more horizontally to prevent injury to the facial nerve.

9. Styloid process 2.5 cm in length. Slender, pointed piece of bone below the ear. Projects down & forwards from inf surface of temporal bone. Proximal tympanohyal part is ensheathed by vaginal process of tympanic bone. Distal stylohyal part gives attachment to – Ligaments – stylohoid & s tylomandibular Muscles – styloglossus , stylohyoid & stylopharyngeal

10. Styloid process cont …. Stylomandibular ligament is a specialised band of cervical fascia which extends from anterior surface of apex of styloid process to the posterior surface of the angle of mandible. This ligament separates parotid gland from submandibular gland & medial pterygoid muscle. Eagle syndrome is characterised by recurrent pain in the oropharynx and face due to elongated styloid process or calcified stylohyoid ligament which interferes with adjacent anatomical structures giving rise to pain.

11. Temporal bone cont …. Petrosa can be seen in superior, medial and posterior views. From superior view, landmarks seen are – Arcuate eminence (corresponding to sup scc ) Tegmen tympani Foramen spinosum (for middle meningeal art) Facial hiatus (marking GPN departure from GG) Petrous ridge (sup petrosal sinus resides on it) Lesser petrosal nerve + superior tympanic artery = occupies superior tympanic canaliculus that lies lateral and parallel to the path of GPN to petrous apex. Petrous apex points anteromedially and is marked by the transition of the intrapetrous to the intracranial ICA, orifice of bony ET & ganglion of trigeminal nerve in meckels cave anterolaterally .

12. Temporal bone cont …. Arcuate eminence – Key landmark in MCF surgeries where IAM can be identified. The bone anteromedial to AA & GSPN is the meatal plane and lies above the IAC. It is often marked by a shallow depression. In this region, dura is firmly attached on medial side & loosely attached on lateral side Meckel’s cave – In trigeminal neuralgia cases, glycerol injection is given in gasserion ganglion located in this area.

13. Temporal bone cont …. Medial view of temporal bone – Porus of IAC ICA exits at petrous apex through internal carotid foramen Deep sulcus posteriorly – sigmoid portion of lateral venous sinus Sulcus at posterior & middle fossa faces of temporal bone – superior petrosal sinus runs in it. Cochlear aqueduct Vestibular aqueduct Mastoid process Styloid process Jugular fossa

14. Temporal bone cont …. Posterior view – Posterior face of petrosa dominates Lies between superior & inferior petrosal sinuses It forms ant border of post cranial fossa. Landmarks – Porus of IAC Operculum Endolymphatic fossette cradling endolymphatic sac Subarcuate fossa

15. Temporal bone cont …. Sigmoid sulcus is an indentation at the lateral aspect of post surface and accommodates sigmoid sinus. Anterior to SS, lies the foveate fossa for intradural portion of endolymphatic sac. Operculum, a ledge at the superior extent of the fossa covers intraosseous portion of endolymphatic sac. Vestibular aqueduct runs anteriorly, medially & superiorly from operculum to end at the medial wall of vestibule. Sup petrosal sulcus at the interface between MCF & PCF plates of temporal bone carries SPS from SS.

16. Temporal bone cont …. Inferior surface – Interfaces with sphenoid & occipital bones. Provides attachment for deep muscles of neck Jugular fossa – houses jugular bulb, separated from ICA by jugulocarotid crest. Inferior tympanic artery & jacobson’s nerve passing through aperture of inferior tympanic canaliculus , is seen in the jugulocarotid crest Cranial aperture of cochlear aqueduct – anteromedial to jugular fossa Groove for inferior petrosal sinus – near petrous apex

17. Temporal bone cont …. Stylomastoid foramen – posterior to styloid process. Occipital artery – occipital groove Digastric muscle – mastoid incisure Jugular foramen Contents – IX, X, XI cranial nerves + Post meningeal art + Inf petrosal & sigmoid sinuses. Medial aspect of the tip IJV & JB are removed

18. Temporal bone cont …. Classically, jugular foramen has been divided into anteromedial pars nervosa consisting IX, X, XI CN and posterolateral pars venosa containing the jugular vein. Styloid process lies lateral to jugular foramen. Glomus jugulare tumours are rare, slow-growing, hypervascular tumors that arise within the jugular bulb. Phelp’s sign – loss of crest of bone as seen in CT between carotid canal & jugular canal in glomus jugulare .

19. Temporal bone cont …. In jugular fossa IX CN lies more ant & lat X, XI CN are located post & med to IX CN CN XI is generally identified as it crosses over IJV in the neck & lat pr of atlas. Sometimes, it can pass medial to IJV. When approached intracranially , IX CN is found in the a anteromed compartment & X, XI CN are posterolateral. Hence it is suggested to consider jugular fossa as a canal rather than an opening so that the IX CN courses from anteromedial to anterolateral as it passes out of the skull making X & XI CN lying posterolateral initially and then posteromedially .

20. Temporal bone cont …. Hypoglossal canal – Located in the anterior portion of occipital condyle & anteroinferior to the jugular foramen. Carries XII cranial nerve that courses medial to cranial nerve X and inferior to jugular foramen. Inferior petrosal sinus – Drains into anterior aspect of jugular bulb. Runs inferior & medial to IX cranial nerve Runs superior & lateral to X, XI cranial nerves

21. Temporal bone cont …. Cochlear aqueduct – Runs from medial aspect of scala tympani of basal cochlear turn to terminate anteromedial to the jugular bulb lying parallel & inf to IAC. In translabyrinthine CPA tumor surgery, drilling medial to jugular bulb opens it and CSF flows into mastoid decompressing CSF pressure. IX nerve, inf petrosal sinus are found immediately inferior to the lateral terminus of it ( X & XI also in some cases ). Therefore, it can be used as a guide to the lower limits of IAC dissection in translabyrinthine approach as it allows full exposure of IAC without risking the lower cranial nerves .

22. Temporal bone cont …. INNER EAR – Bony labyrinth houses sensory organs & soft tissue structures of the inner ear and consists of cochlea, 3 scc & vestibule. Bone has 3 layers – inner endosteal , outer periosteal & middle layer consisting of endochondral and intrachondrial bone. Cochlea spirals 2.5 turns about its central axis, the modiolus and height of it is 5mm. Base of cochlea abuts the fundus of IAC & is perforated by cochlear nerve fibres.

23. Temporal bone cont …. Apex lies medial to tensor tympani muscle. Osseous spiral lamina winds around the modiolus and along with basilar membrane separates scala media from scala tympani. Interscalar septum separates adjacent turns of cochlea. 3 scc – superior, posterior & lateral are orthogonally related to one another and arc over a span of 240 degrees. Each canal has an ampullated (2mm) & a nonampullated (1mm) end. Ampulla is cribrose for passage of nerve fibres. Nonampullated ends of posterior & superior scc fuse to form crus commune.

24. Temporal bone cont …. All ends open into the vestibule. Solid angle – angle formed by the 3 scc Trautmanns triangle – bony labyrinth, sigmoid sinus & superior petrosal sinus are the boundaries. Thinning or frank dehiscence of the bone of superior scc may cause sound or pressure induced vertigo. Vestibule is the central chamber of labyrinth & is 4mm in diameter . Medial wall of vestibule – spherical recess for saccule & elliptical recess for utricle and a cochlear recess for cochlear duct .

25. Temporal bone cont …. Mike’s dot – (macula cribrosa superior) :- passageway for superior vestibular nerve fibres to the cristae ampullares of lateral and superior scc . It is an important landmark in translabyrinthine surgery as it corresponds to the extreme lateral aspect of IAC. Fissures in bony labyrinth – 3 in number. Fissula ante fenestrum - evagination of the perilymphatic space anterosuperior to oval window, filled with fibrous tissue & cartilage in adult Fossula post fenestrum – perilymphatic evagination posterior to oval window. Hyrtle’s fissure ( tympanomeningeal hiatus) – embryologic remnant.

26. Temporal bone cont …. Microfissures – 2 in number. 1) between round window niche & ampulla of posterior scc 2) superior & inferior to oval window. Microfissures are breaks in the endosteal and enchondral layers of temporal bone, and filled with fibrous tissue & acellular matrix. Hyrtle’s fissure if persistent is a route of CSF leakage into ME. Other fissures are hypothesised to be the routes of perilymph leakage.

27. Temporal bone cont …. Membranous labyrinth consists of cochlear duct, 3 scd & their cristae ampullares , otolithic organs like utricle & saccule, endolymphatic duct & sac. Space between bony & membranous labyrinths are filled with connective tissue, blood vessels, perilymph + s.tympani , s.vestibuli , perilymphatic cistern of vestibule, perilymphatic duct, perilymph spaces surrounding the scd . Endolymphatic duct originates in med wall of vestibule. It first parallels crus commune & then posterior scc as it heads to endolymphatic sac, anterior & medial to sigmoid sinus.

28. Temporal bone cont …. Endolymphatic sac lies 10mm inferior & lateral to porus of IAC. It has an intraosseous portion covered by operculum and a more distal intradural portion. Donaldson’s line – a surgical landmark in endolymphatic sac surgery, is derived by extending the plane of the lateral scc so that it bisects the posterior scc and contacts the posterior fossa dura . Endolymphatic sac lies inferior to this line.

29. Temporal bone cont …. IAC – Contents – superior & inferior vestibular nerves, cochlear nerve, facial & intermediate nerves, labyrinthine artery & vein. 3.4mm diameter, 8mm length. Porus – PCF opening & fundus – labyrinth opening. At the fundus -

30. Temporal bone cont …. The nerves rotate as we progress medially, with fusion of the cochlear & vestibular nerves. Facial nerve comes to lie anterior to vestibulocochlear bundle Cochlear nerve moves to lie inferior to the vestibular nerve. Bill’s bar – important landmark in translabyrinthine surgery of CPA tumor as it separates SVN from anteriorly located facial nerve.

31. NEUROANATOMY TRIGEMINAL NERVE – Gasserian ganglion of trigeminal nerve occupies meckel’s cave on middle cranial fossa face of the temporal bone, anterolateral to the petrous apex. SUP VIEW SAGITTAL VIEW

32. NEUROANATOMY cont …. ABDUCENS NERVE – Abducens nerve runs in dorello’s canal beneath posterior petroclinoid ( gruber’s ) ligament. Petrous apicitis can manifest with purulent otorrhea , retro-orbital pain and VI nerve palsy .

33. NEUROANATOMY cont …. FACIAL NERVE – Innervates structures derived from Reichert’s cartilage. 3 nuclei give rise to its fibres – Motor nucleus in caudal pons Superior salivatory nucleus dorsal to motor nucleus Nucleus tractus solitarius in medulla oblongata Superior aspect of the motor nucleus that innervates frontalis and orbicularis oculi, receives input from both sides but inferior portion receives only ipsilateral input.

34. NEUROANATOMY cont …. 5 fibre types make up the trunk of the facial nerve. SVE – facial expression, stapedius , stylohyoid , digastric post belly GVE – lacrimal, nasal cavity seromucinous , submaxillary , sublingual Taste ( sensory ) fibres from ant 2/3 rd tongue, tonsillar fossae, posterior palate Somatic sensory from EAC & concha Visceral afferent from mucosa of nose, pharynx, palate.

35. NEUROANATOMY cont …. Course of the facial nerve is divided into 5 segments. Intracranial segment – 24mm from pons to the porus of IAC Intracanalicular segment – traverses IAC, occupies anterosuperior quadrant at fundus where it is joined by nervus intermedius . Intralabyrinthine segment – shortest, 4mm, from beginning of fallopian canal to the geniculate ganglion. Tympanic segment – 13mm long, courses in the medial wall of the tympanic cavity, superior to the cochleariform process & oval window. Mastoid segment – 20mm, from 2 nd genu (at lat scc ) to stylomastoid foramen.

36. NEUROANATOMY cont ….

37. NEUROANATOMY cont …. Anomalous courses – Tympanic segment may be anterior and inferior to oval window. Mastoid segment may bulge more posteriorly & laterally than usual. Vertical segment may be bi or tripartite. Fallopian canal dehiscences – Most likely site is tympanic segment over oval window. Subarachnoid space – extends till junction of labyrinthine & tympanic segments. Occasionally it extends into GG or rarely into tympanic segment.

38. NEUROANATOMY cont …. CSF otorrhea may occur in such cases as proposed by Gacek . Branches of facial nerve – Intratemporal – Greater petrosal nerve – arises from anterior aspect of GG & emerges onto floor of MCF via the facial hiatus. Nerve to stapedius – arise from mastoid segment near pyramid. Chorda tympani – 6mm proximal to stylomastoid foramen.

39. NEUROANATOMY cont …. Facial recess – Triangular area inferior to the incudal fossa. Lateral to facial nerve vertical segment. Medial to chorda tympani nerve. Used in intact canal wall mastoidectomy to gain access to ME. Nervus intermedius (nerve of wrisberg ) – Carries taste, secretory & sensory fibres of facial nerve. Runs separate in IAC Occupies dorsal aspect in tympanic segment & posterolateral aspect in mastoid segment.

40. NEUROANATOMY cont …. Cochlear nerve – Arise from spiral ganglion neurons. At the fundus, it is in anteroinferior compartment. Rotates as it heads towards porus Enters brainstem a few mm caudal to root entry zone of V nerve. Vestibular nerves – SVN & IVN occupy posterior half of IAC. SVN innervates superior & lateral scc , utricular macula, superior saccular macula. IVN innervates inferior saccular macula Posterior ampullary br of IVN, separates a few mm away from porus , traverses singular canal to posterior canal ampulla and supplies post scc .

41. NEUROANATOMY cont …. Sensory nerves of tympanomastoid compartment – Jacobson’s nerve (tympanic br of IX nerve) - Arises from petrosal ganglion located in petrosal fossa of jugulocarotid crest Through inferior tympanic canaliculus, enters ME along with inf tymp art Then it climbs the promontory to meet caroticotympanic plexus. Lesser petrosal nerve is formed here by joining of pregaanglionic parasympathetic jacobson fibres with postganglionic sympathetic caroticotympanic plexus. LPN heads to floor of MCF within or parallel to semicanal of tensor tympani. Jacobson’s nerve mediates otalgia from pharynx.

42. NEUROANATOMY cont …. Arnold’s nerve (auricular br of X nerve)- It has fibres from VII, IX & X nerves. Originates in jugular foramen Passes over dome of jugular bulb (via mastoid canaliculus) Enters fallopian canal It has been implicated in herpetic involvement of the EAC in herpes zoster oticus and the cough reflex elicited by manipulation of EAC.

43. VASCULAR ANATOMY Temporal bone arteries – ICA :- Enters temporal bone through external carotid foramen located anteromedial to styloid process. Course in intrapetrous segment – 1 st passes anterior to tympanic cavity & cochlea Then bends (it’s knee) to run medial to ET & inferomedial to semicanal of TT muscle Then it climbs to exit the temporal bone at internal carotid foramen. Venous & sympathetic plexus accompanies it throughout intrapetrous course. Bony shell covering it is very thin (<0.5mm) and dehiscent in 6% cases. In ME surgeries, medial wall of ET gently dissected not to injure ICA.

44. VASCULAR ANATOMY cont …. Anterior Inferior Cerebellar Artery – AICA often extends a loop into the IAC. This may cause symptoms like vertigo & tinnitus. Disruption of AICA causes haemorrhage in and infarction of the labyrinth & brainstem. Temporal bone veins – 3 dominant sinuses are sigmoid, superior petrosal & inferior petrosal. Sigmoid is a portion of lat venous sinus.

45. VASCULAR ANATOMY cont …. Sup sagittal & straight sinuses merge at the internal occipital protuberance. Right and left transverse sinuses extend beyond this junction & lie inferior to the tentorium. Anteriorly, sup petrosal sinus joins the transverse sinus and this junction marks the beginning of sigmoid sinus.

46. VASCULAR ANATOMY cont …. Lateral venous sinus occupies an S-shaped sulcus in posterior mastoid extending from transverse sinus to internal jugular vein. Angle of citelli – angle between sigmoid sinus/ PCF dura and the MCF dura. Superior petrosal sinus drains cavernous into lateral venous. Runs in sup petrosal sulcus at junction of PCF & MCF dural plates. Inferior petrosal sinus Courses in petro-occipital suture line. Drains cavernous into jugular bulb.

47. VASCULAR ANATOMY cont …. Emissary veins are drainage routes of the dural venous sinuses through the skull that communicate with the superficial veins of the scalp. A fairly constant emissary vein, the mastoid emissary vein, can be found at the junction of the temporal and occipital bones and usually communicates with the occipital or postauricular vein. Greisinger’s sign – Tenderness and edema over the mastoid are pathognomonic for suppurative thrombo - phlebitis of the sigmoid sinus and reflect thrombosis of mastoid emissary vein.

48. VASCULAR ANATOMY cont …. Classification-of-the-Superior-Petrosal-Veins-and-Sinus-Based-on-Drainage-Pattern

49. VASCULAR ANATOMY cont …. Arachnoid granulations ( pacchionian bodies) – projections of pia-arachnoid into the venous sinuses & venous lacunae are extensions of subarachnoid space. a lso extend from arachnoid of MCF & PCF into adjacent mastoid air cells. Gacek linked adult onset spontaneous CSF leak to these granulations. Jugular bulb – Between sigmoid sinus & internal jugular vein Has a thin wall that does not contract with bipolar & is prone to rupture High-riding (extending above the level of inferior tympanic annulus) jugular bulbs have a very thin wall (0.1-0.3mm). It encroaches < 2mm inferior to IAC. It may mimic ME vascular mass like glomus tympanicum

50. VASCULAR ANATOMY cont …. Middle ear blood vessels – Inferior tympanic artery Br of ascending pharyngeal ( br of ECA) Traverses inferior tympanic canaliculus with jacobson nerve. Feeder of tympanic paragangliomas Anastomotic network of tympanum – Formed by br of ECA like ant tympanic, deep auricular, mastoid, stylomastoid , superficial petrosal & tubal……

51. VASCULAR ANATOMY cont …. Labyrinthine vessels – Labyrinthine artery Br of AICA Subarcuate artery Br of labyrinthine or AICA or both Passes within arch of sup scc .

52. VASCULAR ANATOMY cont …. Facial nerve vessels – Intrinsic system Runs within the nerve Poorly developed in labyrinthine segment Well developed in tympanic & mastoid segments Extrinsic system AICA supplies intracranial segment Superficial petrosal supplies GG & superior mastoid segment Stylomastoid artery supplies inferior mastoid segment