The middle ear has 6 walls. Posterior wall of the tympanic cavity. Topography of the anterior wall of the tympanic cavity. Clinical anatomy of the tympanic cavity
Tympanic cavity, cavitas tympanica (Fig. , , ; see Fig. , , ), is a slit-like cavity in the thickness of the base of the pyramid of the temporal bone. It is lined with a mucous membrane that covers six of its walls and continues posteriorly into the mucous membrane of the cells of the mastoid process of the temporal bone, and in front into the mucous membrane of the auditory tube.
Outdoor membranous wall, paries membranaceus, the tympanic cavity is formed over a larger extent by the inner surface of the tympanic membrane, above which the upper wall of the bony part of the auditory canal takes part in the formation of this wall.
Internal labyrinth wall, paries labyrinthicus, the tympanic cavity is at the same time the outer wall of the vestibule of the inner ear.
In the upper part of this wall there is a small depression - dimple of the window of the vestibule, fossula fenestrae vestibuli, which has vestibule window, fenestra vestibuli(see Fig. , ), is an oval hole covered by the base of the stapes.
In front of the dimple of the window of the vestibule, on the inner wall, the septum of the muscular-tubal canal ends in the form cochlear process, processus cochleariformis.
Below the window of the vestibule there is a rounded elevation - cape, promontorium, on the surface of which there is a vertically running promontory furrow, sulcus promontorii.
Below and posterior to the cape there is a funnel-shaped snail window dimple, fossula fenestrae cochleae, where the round is located snail window, fenestra cochleae(see fig.).
The dimple of the cochlear window is limited above and behind by a bone ridge - cape stand, subiculum promontorii.
Snail window closed secondary tympanic membrane, membrana tympani secundaria(see fig.). It attaches to the rough edge of this hole - crest window snail, crista fenestrae cochleae.
Above the snail window and behind the promontory is a small depression called tympanic sinus, sinus tympani.
Upper tegmental wall, paries tegmentalis, the tympanic cavity is formed by the bone substance of the corresponding section of the petrous part of the temporal bone, which due to this received the name roof of the tympanic cavity, tegmen tympani. In this place, the tympanic cavity forms an upward-facing epitympanic recess, recessus epitympanicus, and its deepest section was called dome part, pars cupularis.
The lower wall (bottom) of the tympanic cavity is called jugular wall, paries jugularis, due to the fact that the bone substance of this wall takes part in the formation of the jugular fossa. This wall is uneven and contains airways , as well as the opening of the tympanic tubule. The jugular wall bears a small awl-shaped protrusion, prominentia styloidea, which is the base of the styloid process.
Posterior mastoid wall, paries mastoideus, the tympanic cavity has a hole - entrance to the cave, aditus ad antrum. It leads to mastoid cave, antrum mastoideum, which in turn communicates with mastoid cells, cellulae mastoideae.
On the medial wall of the entrance there is an elevation - protrusion of the lateral semicircular canal, prominentia canalis semicircularis lateralis, below it there is an arched line running from front to back and downwards protrusion of the facial canal, prominentia canalis facialis.
In the upper medial section of this wall there is pyramidal eminence, eminentia pyramidalis, with embedded in its thickness stapedius muscle, m. stapedius.
On the surface of the pyramidal elevation there is a small depression - fossa incudis, which includes the short leg of the anvil.
Somewhat below the fossa of the incus, on the anterior surface of the pyramidal eminence, under the prominence of the facial nerve is located posterior sinus, sinus posterior, and below, above the subulate protrusion, it opens tympanic aperture of the canaliculus of the chordae tympani, apertura tympanica canaliculi chordae tympani.
Front carotid wall, paries caroticus, the tympanic cavity carries tympanic cells, cellulae tympanicae. Its lower section is formed by the bone substance of the posterior wall of the canal of the internal carotid artery, above which is located tympanic opening of the auditory tube, ostium tympanicum tubae auditivae.
Clinicians conventionally divide the tympanic cavity into three sections: lower, middle and upper.
TO lower section tympanic cavity ( hypotympanum) include part of it between the lower wall of the tympanic cavity and the horizontal plane drawn through the lower edge of the eardrum.
Middle section tympanic cavity ( mesotympanum) occupies most of the tympanic cavity and corresponds to that part of it that is limited by two horizontal planes drawn through the lower and upper edges of the tympanic membrane.
Upper section tympanic cavity ( epitympanum) is located between the upper border of the middle section and the roof of the tympanic cavity.
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The middle ear (auris media) consists of three parts: the tympanic cavity, the mastoid cavities and the auditory (Eustachian) tube.
The tympanic cavity (cavitas tynpani) is a small cavity, about 1 cm3 in volume. It has six walls, each of which plays a major role in the functions performed by the middle ear.
The tympanic cavity is conventionally divided into three floors: upper (cavum epitympanicum), middle (cavum mesotympanicum) and lower (cavum hypotympanicum). The tympanic cavity is limited by the following six walls.
The outer (lateral) wall is almost entirely represented by the eardrum, and only the uppermost part of the wall is bone. The eardrum (membrana tympani) is funnel-shaped and concave into the lumen of the tympanic cavity; its most retracted place is called the navel (umbo). The surface of the eardrum is divided into two unequal parts. The upper one, the smaller one, corresponding to the upper floor of the cavity, represents the loose part (pars flaccida), the middle and lower ones constitute the tense part (pars tensa) of the membrane.
1 - air-containing cells of the mastoid process; 2 - protrusion of the sigmoid sinus; 3 - cave and cave roof; 4 — protrusion of the ampulla of the external (horizontal) semicircular canal; 5 - protrusion of the facial nerve canal; 6 - muscle that stretches the tympanic membrane; 7— cape; 8 - window of the vestibule with the base of the stapes; 9 — cochlear window; 10 - stapes muscle located in the canal; 11 - facial nerve after exiting through the stylomastoid foramen
The structure of these parts, unequal in surface area, is also different: the loose part consists of only two layers - the outer, epidermal, and internal, mucous, and the tense part has an additional middle, or fibrous, layer. This layer is represented by fibers that are closely adjacent to each other and have a radial (in the peripheral parts) and circular (central part) arrangement. The handle of the hammer is woven into the thickness of the middle layer, and therefore it repeats all the movements made by the eardrum under the influence of the pressure of the sound wave penetrating the external auditory canal.
1 - tensioned part; 2 - fibrocartilaginous ring; 3 — light cone; 4 - navel; 5 — hammer handle; 6 - anterior fold of the malleus; 7 - short process of the malleus; 8 - posterior fold of the malleus; 9 - relaxed part of the eardrum; 10 — head of the hammer; 11 — anvil body; 12 - long leg of the anvil; 13 - tendon of the stapedius muscle, visible through the eardrum.
Eardrum quadrants: A - anteroinferior; B - posteroinferior; B - posterosuperior; G - anterosuperior
On the surface of the tympanic membrane, a number of “identifying” elements are distinguished: the handle of the malleus, the lateral process of the malleus, the navel, the light cone, the folds of the malleus - anterior and posterior, delimiting the tense part of the tympanic membrane from the relaxed part. For the convenience of describing certain changes in the eardrum, it is conventionally divided into four quadrants.
In adults, the eardrum is located at an angle of 450 in relation to the lower wall, in children - about 300.
Inner (medial) wall
The protrusion of the main curl of the cochlea, the promontory, protrudes into the lumen of the tympanic cavity on the medial wall. Behind and above it is visible the window of the vestibule, or oval window (fenestra vestibuli) in accordance with its shape. Below and behind the promontory is the window of the cochlea. The window of the vestibule opens into the vestibule, the window of the cochlea opens into the main curl of the cochlea. The window of the vestibule is occupied by the base of the stapes, the window of the cochlea is closed by the secondary tympanic membrane. Directly above the edge of the fenestra vestibule there is a prominence of the facial nerve canal.Upper (tire) wall
The upper (tegmental) wall is the roof of the tympanic cavity, delimiting it from the middle cranial fossa. In newborns, there is an open fissure (fissura petrosqumosa), which creates direct contact of the middle ear with the cranial cavity, and with inflammation in the middle ear, irritation of the meninges is possible, as well as the spread of pus from the tympanic cavity to them.The lower wall is located below the level of the lower wall of the auditory canal, so there is a lower floor of the tympanic cavity (cavum hypotympanicum). This wall borders the bulb of the jugular vein.
Back wall
In the upper section there is an opening connecting the tympanic cavity with the permanent large cell of the mastoid process - the cave; below there is an elevation from which the tendon of the stapedius muscle emerges and is attached to the neck of the stapes. Contraction of the muscle promotes movement of the stapes towards the tympanic cavity. Below this protrusion there is a hole through which the chorda tympani (chorda tympani) departs from the facial nerve. It leaves the tympanic cavity, passing the auditory ossicles, the petrotympanic fissure (fissura petrotympanica) in the area of the anterior wall of the external auditory canal, near the temporomandibular joint.Front wall
In its upper part there is an entrance to the auditory tube and a canal for the muscle that moves the stapes towards the vestibule (m. tensor tympani). It borders on the canal of the internal carotid artery.There are three auditory ossicles in the tympanic cavity: the malleus (malleus) has a head connected to the body of the incus, a manubrium, and a lateral and anterior process. The manubrium and lateral process are visible when examining the tympanic membrane; the anvil (incus) resembles a molar, has a body, two legs and a lenticular process, the long leg is connected to the head of the stapes, the short one is placed at the entrance to the cave; The stirrup (stapes) has a base (area 3.5 mm2), two legs forming an arch, a neck and a head. The auditory ossicles are connected to each other through joints, which ensures their mobility. In addition, there are several ligaments that support the entire chain of auditory ossicles.
The mucous membrane is mucoperiosteum, lined with squamous epithelium, and does not normally contain glands. Innervated by branches of sensory nerves: trigeminal, glossopharyngeal, vagus, and facial.
The blood supply to the tympanic cavity is carried out by the branches of the tympanic artery.
Mastoid
The mastoid process (processus mastoideus) acquires all its details only by the 3rd year of a child’s life. The structure of the mastoid process varies from person to person: the process can have many air cells (pneumatic), consist of spongy bone (diploetic), or be very dense (sclerotic).Regardless of the type of structure of the mastoid process, it always has a pronounced cavity - a cave (antrum mastoideum), which communicates with the tympanic cavity. The walls of the cave and individual cells of the mastoid process are lined with mucous membrane, which is a continuation of the mucous membrane of the tympanic cavity.
Eustachian tube (tuba auditiva)
It is a 3.5 cm long canal connecting the tympanic cavity with the nasopharynx. The auditory tube, like the external auditory canal, is represented by two sections: bone and membranous-cartilaginous. The walls of the auditory tube move apart only when swallowing, which provides ventilation to the cavities of the middle ear. This is accomplished through the work of two muscles: the levator soft palate muscle and the tensor soft palate muscle. In addition to ventilation, the auditory tube also performs drainage (removal of transudate or exudate from the tympanic cavity) and protective functions (the secretion of the mucous glands has bactericidal properties). The mucous membrane of the tube is innervated by the tympanic plexus.Yu.M. Ovchinnikov, V.P. Gamow
Posterior wall of the tympanic cavity(paries mastoideus) borders the mastoid process. It is the longest wall - its length reaches 15 mm, and its height is 13-14 mm (E. B. Neustadt). In the upper section there is no wall; it is replaced by the aditus ad antrum. Underneath it the wall is uneven, there is a depression to which the short process of the incus is adjacent, just below, on the outer surface of the pyramidal protrusion there is a hole through which the tympanic chord enters the cavity, extending from the facial nerve just before it exits the stylomastoid foramen.
The pyramid itself projection, extending from the posterior wall below the aditus, is described together with the medial wall of the tympanic cavity. The posterior wall is often delimited from the bottom of the tympanic cavity by prominentia styloidea, a small bony protrusion formed due to the fact that the apophysis of the styloid process raises the wall of the tympanic cavity. In the depths of the posterior wall there passes the canal of the facial nerve and the cells surrounding it.
Anterior wall of the tympanic cavity(paries caroticus) so imperceptibly passes into the medial that it can be considered as part of the latter. Wall height 5-9 mm, width 3-4.5 mm (E. B. Neustadt). The upper half of the wall is occupied by the mouth of the Eustachian tube, and the lower half is represented by a thin bone plate that separates the tympanic cavity from the ascending segment of the internal carotid artery (its first bend) and the surrounding venous and sympathetic nerve plexus.
In a sleepy channel the artery is enveloped by the dura mater. According to V.F. Vilkhony, in most cases the ascending part of the canal has an oblique direction, from bottom to top and from back to front, less often the direction of the canal approaches vertical. In general, the direction of the canal basically coincides with the length of the external auditory opening. The projection line of the emerging part of the carotid cap on the outer surface of the temporal bone in the area of its tympanic part runs from the base of the styloid process to the root of the zygomatic process, parallel to the length of the external auditory foramen.
Bone plate(the outer wall of the canal of the internal carotid artery) also separates the ascending segment of the artery from the bony part of the Eustachian tube, which passes lateral to the carotid artery. It is practically important to know that the internal carotid artery does not pulsate in the bone canal. This is due to the fact that when entering the bone, the artery stack loses elastic tissue, remaining only muscle (Ramadier). For the most part, in the anterior wall there are small pneumatic cells located radially, surrounding the carotid artery and the bone section of the tube.
Sometimes the carotid canal protrudes more into the tympanic cavity, as if pushing the promontory back. The bone plate separating the internal carotid artery from the mucous membrane of the tympanic cavity is penetrated by thin tubules (canaliculi carotico-tympaiiici) and often has dehiscence; In rare cases, these wall defects are so significant that there is a risk of arterial injury during paracentesis.
In one case, through a large perforation tympanic membrane, pulsation of the internal carotid artery was observed. With purulent otitis media (especially with an exacerbation of the chronic process), the possibility of infection being transferred through the veins that form the plexus surrounding the carotid artery into the cavernous sinus with which these veins communicate cannot be ruled out. Infection from the tympanic cavity can also pass through the carotid tympanic tubules and dehiscence to the wall of the carotid artery and ultimately cause its arrosion, followed by fatal bleeding.
The same bleeding may be a consequence of caries of the anterior stack (especially middle ear tuberculosis), as well as accidental injury to the artery during surgery for petrositis. Bleeding only from the venous plexus in the carotid canal is possible both with caries of the pyramid and during surgery to remove the gasserian node. With purulent otitis media, thrombosis of the internal carotid artery with subsequent cerebral embolism is also possible.
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cavities
The middle ear consists of a number of interconnected air cavities: tympanic cavity(cavum tympani), auditory tube(tuba auditiva), entrance to the cave(aditus ad antram), caves(antrum) and related air cells of the mastoid process(cellulae mastoidea). The middle ear communicates with the nasopharynx through the auditory tube. Under normal conditions, this is the only communication between all cavities of the middle ear and the external environment.
Tympanic cavity
The tympanic cavity can be compared to an irregularly shaped cube with a volume of up to 1 cm." It has six walls: upper, lower, anterior, posterior, outer and inner.
Walls of the tympanic cavity:
Upper wall, or the roof of the tympanic cavity (tegmen tympani) is represented by a bone plate with a thickness of 1 to 6 mm. It separates the chickpea cavity from the middle cranial fossa. There are small holes in the roof through which vessels pass that carry blood from the dura mater to the mucous membrane of the middle ear. Sometimes there are dehiscences in the upper wall. In these cases, the mucous membrane of the tympanic cavity is directly adjacent to the dura mater.
The lower (jugular) wall, or the bottom of the tympanic cavity is in contact with the underlying jugular fossa, in which the bulb of the jugular vein is located. The lower wall may be very thin or have dehiscences, through which the vein bulb sometimes protrudes into the tympanic cavity, this explains the possibility of wounding the vein bulb during surgery.
ENT diseases
Front wall(tubal or carotid) is formed by a thin bone plate, outside of which is the internal carotid artery. There are two openings in the anterior wall, the upper of which is narrow and leads into the hemicanal (semicanalis m.tensoris thympani), and the lower, wide, into the tympanic opening of the auditory tube (ostium tympanicum tubae auditivae). In addition, the anterior wall is penetrated by thin tubules (canaliculi caroticotympanici). through which vessels and nerves pass into the tympanic cavity. In some cases it has dehiscence.
Back wall(mastoid) 1 borders the mastoid process. In the upper part of this wall there is a wide passage (aditus ad antrum), connecting the supratympanic space (attic) with the permanent cell of the mastoid process - the cave (antrum). Below this passage there is a protrusion - a pyramidal process, from which the stapedius muscle (m.stapedius) begins. On the outer surface of the pyramidal process there is a tympanic foramen, through which the tympanic chord, extending from the facial nerve, enters the tympanic cavity. The descending limb of the facial nerve canal passes through the thickness of the posterior part of the lower wall.
Outer (membranous) wall formed by the eardrum and partly in the attic area by a bone plate that extends from the upper bony wall of the external auditory canal.
Internal (labyrinthine, medial) wall is the outer wall of the labyrinth and separates it from the cavity of the middle ear. On this wall in the middle part there is an oval-shaped elevation - a promontory (promotorium), formed by the protrusion of the main curl of the cochlea. Posterior and superior to the promontory there is a niche for the window of the vestibule (oval window), closed by the base of the stapes. The latter is attached to the edges of the window by means of an annular ligament. Posterior and inferior to the promontory is another niche, at the bottom of which is the fenestra cochlea (round window), leading into the cochlea and closed by the secondary tympanic membrane. Above the window of the vestibule on the inner wall of the tympanic cavity, in the direction from front to back, a horizontal bend of the bony canal of the facial nerve (fallopian canal) passes.
Tympanic cavity(cavum tympani) represents the space enclosed between the eardrum and the labyrinth. The shape of the tympanic cavity resembles an irregular tetrahedral prism with a volume of about 1 cm 3, with the largest upper-lower dimension (height) and the smallest between the outer and inner walls (depth). In the tympanic cavity there are six walls(Fig. 5.5):
External and internal;
Top and bottom;
Front and back.
Outer (lateral) wall is represented by the tympanic membrane, separating the tympanic cavity from the external auditory canal, and the bone sections bordering it above and below (Fig. 5.6). Up from the tympanic membrane, the plate of the upper wall of the external auditory canal, 3 to 6 mm wide, is involved in the formation of the lateral wall, to the lower edge of which (incisura Rivini) the eardrum is attached. Below level
Rice. 5.5. Schematic representation of the tympanic cavity (no outer wall): a - inner wall; b - front wall; c - rear wall; g - bottom wall; d - upper wall; 1 - lateral semicircular canal; 2 - facial canal; 3 - roof of the tympanic cavity; 4 - window of the vestibule; 5 - hemicanal of the tensor tympani muscle; 6 - tympanic opening of the auditory tube; 7 - canal of the carotid artery; 8 - cape; 9 - tympanic nerve; 10 - bulb of the internal jugular vein; 11 - cochlear window; 12 - drum string; 13 - pyramidal elevation; 14 - entrance to the cave
At the attachment of the eardrum there is also a small bone sill.
In accordance with the structural features of the lateral wall, the tympanic cavity is conventionally divided into three departments: top, middle and bottom.
Upper section - epitympanic space, attic, or epitympanum - located above the upper edge of the stretched part of the eardrum. Its lateral wall is the bony plate of the upper wall of the external auditory canal
Rice. 5.6. Lateral (outer) wall of the tympanic cavity: 1 - supratympanic recess; 2 - superior ligament of the malleus; 3 - hammer handle; 4 - eardrum; 5 - tympanic opening of the auditory tube; 6 - knee of the internal carotid artery; 7 - second (vertical) knee of the facial nerve; 8 - drum string; 9 - anvil
And pars flaccida eardrum. In the supratympanic space there is an articulation between the malleus and the incus, which divides it into external and internal sections. In the lower part of the outer section of the attic, between pars flaccida The tympanic membrane and the neck of the malleus are the superior recess of the mucous membrane, or Prussian's space. This narrow space, as well as the anterior and posterior pockets of the tympanic membrane (Treltsch's pouches) located downward and outward from the Prussian space, require mandatory revision during surgery for chronic epitympanitis in order to avoid relapse.
Middle section tympanic cavity - mesotympanum - largest in size, corresponds to the projection pars tensa eardrum.
Lower section(hypotympanum)- a depression below the level of attachment of the eardrum.
Medial (internal, labyrinthine, promontorial) wall The tympanic cavity separates the middle and inner ear (Fig. 5.7). In the central section of this wall there is a protrusion - a promontory, or promontorium, formed by the lateral wall of the main curl of the cochlea. The tympanic plexus is located on the surface of the promontorium (plexus tympanicus). The tympanic (or Jacobson) nerve participates in the formation of the tympanic plexus (n. tympanicus - branch n. glossopharyngeus), nn. trigeminus, facialis, as well as sympathetic fibers from plexus caroticus internus.
Behind and above the cape is vestibule window niche (fenestra vestibuli), shaped like an oval, elongated in the anteroposterior direction, measuring 3 by 1.5 mm. The vestibule window is closed base of the stirrup (basis stapedis), attached to the edges of the window
Rice. 5.7. The medial wall of the tympanic cavity and the auditory tube: 1 - promontory; 2 - stirrup in the niche of the window of the vestibule; 3 - cochlear window; 4 - first knee of the facial nerve; 5 - ampulla of the lateral (horizontal) semicircular canal; 6 - drum string; 7 - stapedius nerve; 8 - jugular vein; 9 - internal carotid artery; 10 - auditory tube
by using annular ligament (lig. annulare stapedis). In the area of the posterior-inferior edge of the promontory there is snail window niche (fenestra Cochleae), protracted secondary tympanic membrane (membrana tympani secundaria). The window niche of the cochlea faces the posterior wall of the tympanic cavity and is partially covered by the projection of the posteroinferior slope of the promontorium.
Directly above the window of the vestibule in the bony fallopian canal there passes the horizontal knee of the facial nerve, and above and posteriorly there is a protrusion of the ampulla of the horizontal semicircular canal.
Topography facial nerve (n. facialis, VII cranial nerve) has important practical significance. Joining with n. statoacousticus And n. intermedius into the internal auditory canal, the facial nerve passes along its bottom, in the labyrinth it is located between the vestibule and the cochlea. In the labyrinthine section, it departs from the secretory portion of the facial nerve greater stony nerve (n. petrosus major), innervating the lacrimal gland, as well as the mucous glands of the nasal cavity. Before exiting into the tympanic cavity, above the upper edge of the window of the vestibule there is geniculate ganglion (ganglion geniculi), in which the taste sensory fibers of the intermediate nerve are interrupted. The transition of the labyrinthine section to the tympanic section is designated as first genus of the facial nerve. The facial nerve, reaching the protrusion of the horizontal semicircular canal on the inner wall, at the level pyramidal eminence (eminentia pyramidalis) changes its direction to vertical (second knee) passes through the stylomastoid canal and through the foramen of the same name (for. stylomastoideum) extends to the base of the skull. In the immediate vicinity of the pyramidal eminence, the facial nerve gives off a branch to stapedius muscle (m. stapedius), here it departs from the trunk of the facial nerve drum string (chorda tympani). It passes between the malleus and the incus through the entire tympanic cavity from above the eardrum and exits through fissura petrotympanica (s. Glaseri), giving taste fibers to the anterior 2/3 of the tongue on its side, secretory fibers to the salivary gland and fibers to the nerve vascular plexuses. The wall of the facial nerve canal in the tympanic cavity is very thin and often has dehiscence, which determines the possibility of inflammation spreading from the middle ear to the nerve and the development of paresis or even paralysis of the facial nerve. Various locations of the facial nerve in the tympanic and mastoid
its departments should be taken into account by the otosurgeon so as not to injure the nerve during the operation.
Located anteriorly and above the window of the vestibule snail-shaped protrusion - proc. cochleariformis, through which the tendon of the tensor tympani muscle bends.
Front wall tympanic cavity - tubal or carotid (paries tubaria s. caroticus). The upper half of this wall is occupied by two openings, the larger of which is the tympanic opening of the auditory tube. (ostium tympanicum tubae auditivae), above which the hemicanal of the tensor tympani muscle opens (m. tensor tympani). In the lower section, the anterior wall is formed by a thin bone plate separating the trunk of the internal carotid artery, passing in the canal of the same name. This wall is penetrated by thin tubules through which vessels and nerves pass into the tympanic cavity, and the inflammatory process can move from the tympanic cavity to the carotid artery.
Back walltympanic cavity- mastoid (paries mastoideus). In its upper section there is a wide passage (aditus ad antrum), through which the epitympanic space communicates with cave (antrum mastoideum)- permanent cell of the mastoid process. Below the entrance to the cave, at the level of the lower edge of the window of the vestibule, on the back wall of the cavity there is pyramidal eminence (eminentia pyramidalis), containing m. stapedius the tendon of which protrudes from the top of this elevation and is directed to the head of the stapes. Outside the pyramidal eminence there is a small hole from which the drum string emerges.
Top wall- roof of the tympanic cavity (tegmen tympani). This is a bone plate with a thickness of 1 to 6 mm, separating the tympanic cavity from the middle cranial fossa. Sometimes there are dehiscences in this plate, due to which the dura mater of the middle cranial fossa is in direct contact with the mucous membrane of the tympanic cavity. This may contribute to the development of intracranial complications in otitis media. In children of the first years of life, at the border of the stony and scaly parts of the temporal bone in the area of the roof of the tympanic cavity there is an unfused fissura petrosquamosa, which makes it possible for brain symptoms (meningismus) to occur in acute otitis media. Subsequently, a seam is formed at the site of this gap - sutura petrosquamosa.
Bottom walltympanic cavity- jugular (paries jugularis)- borders on the underlying bulb of the jugular vein (bulbus venae juggle). The bottom of the cavity is located 2.5-3 mm below the edge of the eardrum. The more the jugular vein bulb protrudes into the tympanic cavity, the more convex the bottom is and the thinner it is. Sometimes bone defects are observed here - dehiscence, then the bulb of the jugular vein protrudes into the tympanic cavity and can be injured when performing paracentesis.
