Indian Journal of Otology

LEAD ARTICLE
Year
: 2020  |  Volume : 26  |  Issue : 3  |  Page : 115--121

Middle ear mucosal compartm


Mahendra Kumar Taneja 
 Department of ENT, Indian Institute of Ear Diseases, New Delhi, India

Correspondence Address:
Dr. Mahendra Kumar Taneja
Department of ENT, Indian Institute of Ear Diseases, New Delhi
India

Abstract

Mucosal folds of middle ear are not a significant barrier in spread of infection cholesteatoma spread towards the least resistance and usually follow the folds. The mucosa of the middle ear is continuous with that of the pharynx via Eustachian tube. It covers the ossicles, muscles, nerves and forms the inner layer of tympanic membrane. Mucosal fold are of two types Composite Fold – these are of ligament with lining mucosa. Duplicate Fold – Fusion of two expanding sacs in absence of any interposing structure. Epitympanic Diaphragm it is an oblique dividing septum between the posterior superior attic and anteroinferior mesotympanium. It comprises of anterior malleolar ligament, lateral malleolar ligament, posterior malleolar ligament, lateral incudal fold, tensor tympani fold and posterior incudal ligament fold. Tympanic Isthimus is 2.5 mm elongated narrow space in epitympanic diaphragm present naturally and provides ventilation. Key message is tensor tympani fold and anterior Pouch of VonTroltsch is responsible for ventilation of anterior compartment. It is extremely important to understand and restore the functional anatomy, proper gas exchange and mucosal clearance from the middle ear compartment. The obstruction site is at tympanic isthimus. It is crucial to visualise and clearance of disease to restore ventilation. In surgical procedures of ear just removal of tensor tympani fold along with resection of Cog provides good results by providing ventilation of attic, mastoid air cells and a successful tympanoplasty.



How to cite this article:
Taneja MK. Middle ear mucosal compartm.Indian J Otol 2020;26:115-121


How to cite this URL:
Taneja MK. Middle ear mucosal compartm. Indian J Otol [serial online] 2020 [cited 2021 Jan 16 ];26:115-121
Available from: https://www.indianjotol.org/text.asp?2020/26/3/115/304284


Full Text



Mucosal folds of middle ear are not a significant barrier in the spread of infection, but cholesteatoma spreads toward the least resistance and usually follow the folds. In long-standing Eustachian tube dysfunction, adhesion formation, chronic otitis media, granulation, and Polyp block the tympanic isthmus. These factors result in the failure of attic ventilation, impairment of hearing, and long-term sequelae. Hence, it is extremely important to understand and correct the microanatomy of mucosal folds thus airway/ventilation of middle ear compartments.

The tympanic cavity is considered an expansion of pharynx. The mucosa of the middle ear is continuous with that of the pharynx via Eustachian tube. It covers the ossicles, muscles, and nerves and forms the inner layer of tympanic membrane. It also covers the mastoid antrum and air cells and forms various middle ear compartments.

It is from the 3rd to 7th fetal month the development of middle ear mucosal compartment takes place. Mucosa originates from the dorsal end of the endoderm of the first pharyngeal pouch. There is outpouching of the endothelium with gradual absorption of mesenchymal tissue. The tympanic cavity develops by outward extension of the endothelium-lined fluid pouch (tubotympanic recess) extending from the Eustachian tube into the cleft. This invagination buds into four sacci and enlarges by replacing the preexisting mesenchyme. The mesenchyme simultaneously transforms into ligament, ossicles, and blood vessels supplying the middle ear cavity and forms various compartments.[1]

From the first pharyngeal groove, the external auditory canal is developed. From the first arch cartilage, the head of malleus, short process, and body of incus are formed. From the second arch cartilage, the handle of malleus, long process of incus, stapes-head, neck, and crura develop. Foot plate develops as a part of otic capsule.

The mucosal fold are of two types:

Composite fold – These are of ligament with lining mucosaDuplicate fold – Fusion of two expanding sacs in the absence of any interposing structure.

 Structure of Middle Ear Compartment



(1) Malleus, (2) incus, (3) stapes, (4) superior malleolar fold, (5) anterior malleolar fold, (6) lateral malleolar fold, (7) posterior malleolar fold, (8) tensor tympani fold, (9) medial incudal fold, (10) lateral incudal fold, (11) interossicular fold, (12) stapedial folds, (13) posterior incudal ligament, (14) superior incudal ligament, (15) anterior malleolar ligament, (16) posterior malleolar ligament.

Anterior malleolar ligament

It originates from the anterior tympanic spine and petrotympanic fissure. It is inserted at the neck and anterior malleolar process of the malleus. The posterior part is broad, and it forms the anterior boundary of Prussak's space. It is in relation to the anterior segment of chorda tympani nerve and anterior tympanic branch of the maxillary artery [Figure 1].{Figure 1}

Anterior malleolar fold

It arises from the anterior wall of the neck of malleus and inserted on the anterior tympanic spine. It forms the medial boundary of the anterior pouch of Von Troltsch [Figure 2] and [Figure 3].{Figure 2}{Figure 3}

Posterior malleolar fold

It originates from the posterior tympanic spine and inserted at the posterior wall of the neck of malleus and posteromedial aspect of the upper portion of the malleus handle. It merges with lateral incudo malleolar fold and forms the medial wall of the posterior pouch of Von Troltsch. It engulfs the posterior segment of chorda tympani nerve [Figure 3].

Lateral malleolar fold

It originates from the middle portion of the malleus neck and spreads on the inside of the scutum border like a fan. It is confluent posteriorly with the anterior descending border of lateral incudo malleolar fold. It also forms the floor of lateral malleolar space and roof of the Prussak's space. It is usually thick, complete, and strong, hence prevents retraction of pars flaccida and cholesteatoma formation [Figure 4].{Figure 4}

Superior malleolar fold

It originates from the superior surface of the head of malleus, spreads like a fan in transverse (coronal) plane, and inserts in the roof of attic (tegmen tympani). It engulfs the superior malleolar ligament having similar attachments and divides the attic into two parts: smaller anterior attic space and larger posterior attic space [Figure 5].{Figure 5}

Lateral incudo malleolar fold

It is a thin transparent membranous fold. It extends posteriorly up to the body and the short process of incus from the outer side neck of malleus. It lies about 1.0 mm above the lateral malleolar fold or roof of the Prussak's space. It is inserted into the lateral attic wall. This fold divides the upper lateral attic space (incudal space) horizontally into upper lateral attic and lower lateral attic space into two halves. It is about 3.00 mm in length and 0.2 mm in thickness. The anterior end bends inferiorly toward the neck of the malleus and merges with the posterior portion of the lateral malleolar ligament fold, making the posterior limit of lateral malleolar space [Figure 6] and [Figure 7].{Figure 6}{Figure 7}

Tensor tympani fold

It is slightly convex and membranous extending 1.5 mm below the roof of Prussak's space from the bony canal and tendon of tensor tympani muscle to the anteromedial wall of the attic and inserts on the transverse crest and supratubal ridge, may extend up to zygoma. It forms the anterior boundary of the Prussak's space. Medially, it is attached to the bony canal of tensor tympani muscle and laterally to the anterior malleolar ligament. Laterally, it is in close relation with the chorda tympani nerve. It separates the supratubal recess from the anterior epitympanic recess and determines their size. Inclination angle variation 80°–100° is responsible for this variation of size. It is intermingled with the anterior malleolar ligament [Figure 8] and [Figure 9].{Figure 8}{Figure 9}

It results by fusion of saccus anticus and anterior saccule of saccus medius. In most of the cases, this fold is incomplete, hence there is a direct communication from the Eustachian tube and supratubal recess up to the posterior attic and antrum.

Supratubal recess

It is the superior extension of the anterior wall (protympanum) of the middle ear cavity. It is a space below the anterior attic between the tympanic orifice of Eustachian tube and tensor tympani fold. If tensor tympani fold is incomplete, the recess provides a direct communication from the Eustachian tube to the whole attic, incudal fossa, mastoid and provides ventilation [Figure 9].

Anterior epitympanic recess

The anterior epitympanic recess is a hollow space located in the anterior part roof of the middle ear, which usually develops from a solitary cell ranging from 1.0 to 7.0 mm in size. The variation of size is due to the angulation of tensor tympani fold which forms the floor of the anterior tympanic recess. The roof and anterior wall is formed by the upwardly convex floor of the middle cranial fossa. The carotid canal, cochlea, tympanic portion of facial nerve, and genu form the medial boundary.

This is a possible route of infection to mastoid. It can be identified on axial computed tomography scan, synonymously known as anterior attic recess, geniculate sinus, and anterior attic compartment [Figure 9].

Epitympanic diaphragm

It is an oblique dividing septum between the posterior superior attic and anteroinferior mesotympanium. Chatllier and Lemonine introduced this concept in 1946 and Palva revised the concept with the theory of ventilation of middle ear cleft. Attic is ventilated through the opening tympanic isthmus in it. It comprises three ligaments and three folds, namely, anterior malleolar ligament, lateral malleolar ligament, posterior malleolar ligament, lateral incudal fold, tensor tympani fold, and posterior incudal ligament fold.

Tympanic isthmus

It is a 2.5-mm elongated narrow space in the epitympanic diaphragm present naturally, extends anteriorly from the tensor tympani muscle to posterosuperiorly up to the anterior edge of the posterior incudal ligament and pyramidal eminence inferoposteriorly. Vertically, it is around 6 mm. The medial boundary is formed by the medial attic wall and laterally by short process, body of incus, and head of malleus. It is divided into two parts by the medial incudal fold into anterior and posterior tympanic isthmus. To understand and make it simple, the airspace is medial to the incus in the attic (behind in viewing during dissection) [Figure 10].{Figure 10}

Anterior tympanic isthmus

It is a narrow space between the tensor tympani muscle anteriorly and incudostapedial joint posteriorly. The diameter is about 1.0–3.0 mm. It is an important route of aeration, and openly communicates with the anterior epitympanum (superior attic). It is always present.

Posterior tympanic isthmus

It is a narrow inconsistent space between the stapedius muscle and short process of incus. It communicates the epitympanum, the mesotympanum, and the airway through incudal fossa.

Pouch of Von Troltsch

The anterior pouch of Von Troltsch is between the anterior malleolar fold and pars tensa of tympanic membrane, whereas the posterior pouch of Von Troltsch is between the posterior malleolar fold and pars tensa of tympanic membrane.

Medial incudal fold

It is located between the long process of incus and tendon of stapedius muscle extending up to pyramidal eminence [Figure 11].{Figure 11}

Superior incudal fold

It extends anteroposteriorly from the superior surface of the body of incus to tegmen and engulfs the superior incudal ligament. It divides the posterior attic and anterior incudal fossa into lateral and medial compartments [Figure 12].{Figure 12}

Posterior incudal fold

It runs between the posterior incudal ligaments from the incus bone [Figure 13].{Figure 13}

Saccus anticus

It is also known as ant pouch of Von Troltsch. It is a part of anterior attic compartment which lies between the anterior malleolar fold and pars tensa of tympanic membrane. It extends up to the bony canal of the tensor tympani muscle and along with saccus medius forms the tensor tympani fold.

Saccus posticus

This mucosal pouch covers the round window, hypotympanic area, sinus tympani, and lower half of the oval window; it extends along the hypotympanum pneumatizes and the posterior tympanic sinus and forms the stapedial folds.

Saccus medius

It is the biggest mucosal pouch which is further divided into three parts. It pneumatizes the petrous part of the temporal bone and forms the medial part of mastoid air cells:

Anterior saccule: It pneumatizes and is in the anterior compartment of atticMedial saccule: It is also termed Prussak's spacePosterior saccule: It extends medially to the long process of incus posteriorly up to the anterior crus of stapes.

Saccus superior

It extends between the pars tensa and posterior malleolar fold through the handle of malleus and the long process of the incus. It runs over the saccus posticus, stapedial tendon, and inferior incudal space up to the antrum. It pneumatizes the squamous portion of the temporal bone. It forms the lateral part of the mastoid air cell system. It is also termed posterior pouch of Von Troltsch.[2]

Korner's septum – It is formed by the fusion of posterior saccule of the saccus medius and saccus superior intervening with mesenchyme and develops as bony septum.

Prussak's space

It develops as the prolongation of superior saccus, hence is also independent of ventilation through a narrow space of posterior pouch of Von Troltsch. It is bounded superiorly by lateral malleolar fold, anteriorly by anterior malleolar fold, posteriorly by posterior malleolar fold, and open to ventilation through the post pouch of Von Troltsch. The floor is formed by the neck of malleus and laterally by pars flaccida[3] [Figure 3] and [Figure 7].

Stapedial folds

There are five folds around the stapes: (1) anterior stapedial fold – between promontory and anterior crus, (2) posterior stapedial fold lies between the promontory and posterior crus of stapes, (3) superior stapedial fold which lies between the crura and bony Fallopian canal, (4) plica stapedial fold that extends from the posterior crus to pyramidal eminence, and (5) obturator stapedial fold. It is present between the two crura of stapes [Figure 14].{Figure 14}

Once you grab the anatomy of mucosal folds and ligaments, it is extremely important to understand the ventilatory pathways and compartments that how these folds direct the entry of air reaching to the entire mastoid cleft up to the mastoid tip. During the development of ear, as discussed earlier, ear is ventilated by four sacs. The main partition is tympanic diaphragm which separates the upper attic from the Prussak's space and mesotympanum. Let's learn the compartments one by one: the first is superior mucosal fold which divides the upper attic into coronal plane into small anterior and large posterior compartments, second is by tensor tympani fold dividing anterior compartment into anterior malleolar space and anterior epitympanic space, also termed sinus epitympani. Cog a bony landmark to divide these space in anterior attic [Figure 9].

The key message is that the tensor tympani fold and anterior pouch of Von Troltsch are responsible for the ventilation of anterior compartment and formed by saccus anticus.

The posterior compartment is divided sagitally into two sections by superior incudal fold [Figure 15].{Figure 15}

It is divided into posterior medial and posterior lateral compartments. The posterior medial attic space, also called medial incudal space, is medial to ossicles. This space is vertically 6.0 mm from the tip of the long process of incus to tegmen [Figure 16].{Figure 16}

Lateral posterior attic space is narrower is between the lateral attic wall (scutum) and malleus head, incus body, and superior incudal fold, and superiorly by tegmen. This space is further divided into three segments: the lateral incudo malleolar fold which horizontally divides it into upper lateral superior incudal space and lower lateral or inferior incudal space [Figure 6] and [Figure 7].

The most anterior portion of lateral posterior compartment above the Prussak's space anterior to the head of malleus is lateral malleolar space. The lateral malleolar space lies above the lateral malleolar fold, medial boundary by the upper neck and head of malleus, laterally by scutum, anteriorly by anterior malleolar fold, and posteriorly by downward anterior end of the incudo malleolar fold. We can understand that the anterior compartment is ventilated through tensor tympani fold by saccus anticus. Prussak's space, superior incudal space by medial saccule of saccus medius. Medial attic, antrum, mastoid by posterior saccule of saccus medius. Saccus superior ventilates through the post pouch of Von Troltsch to the inferior incudal space and also to the antrum. Saccus posticus being the most caudal ventilates the hypotympanum and retrotympanum (sinus tympani, facial recess, and round window) [Figure 17].[4]{Figure 17}

It is extremely important to understand and restore the functional anatomy, proper gas exchange, and mucosal clearance from the middle ear compartment. The obstruction site is at tympanic isthmus. It is crucial to visualize clearance of disease to restore ventilation. Microscopic view or Pee test (water flow) are usually deceptive, and restoration of airway requires the use of a wide-angle otoendoscope. Hence, correction or corrected Eustachian tube dysfunction alone may not help and fail to provide optimum hearing improvement. In surgical procedures of ear, just removal of the tensor tympani fold along with resection of Cog provides good results by providing ventilation of attic and mastoid air cells. Inadequate mucosal pathways and ventilation may result in air–bone gap in spite of best tympanoplasty. Restoration of proper airway is extremely rewarding in terms of having normal middle ear pressure. It also prevents secondary retraction and perforation.

I conclude it is absolutely essential to learn and practice the temporal bone dissection under otoendoscope. Visualization and focus on mucosal compartment keeping in mind how we can maintain or restore ventilation of mastoid is the key point of successful tympanoplasty.

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Conflicts of interest

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