--- title: "Anatomy of Middle Ear - Walls & Parts" description: "Detailed ENT notes covering Anatomy of Middle Ear - parts, walls, structures, and clinical aspects of the middle ear cavity." source: "The ENT Resident" author: "Dr. Mausumi Das" canonical_url: "https://www.theentresident.com/ent-notes-lectures/middle-ear-anatomy-walls" categories: ["Otology"] video: "https://www.youtube.com/watch?v=cdAte_4qDL4" image: "https://media.theentresident.com/og-images/middle-ear-anatomy-walls.png" --- # Anatomy of Middle Ear - Walls & Parts Detailed ENT notes covering Anatomy of Middle Ear - parts, walls, structures, and clinical aspects of the middle ear cavity. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=cdAte_4qDL4 ## Anatomy of the Middle Ear - Parts & Walls In this post, we'll focus on the **Parts** and **Walls** of the Middle Ear cavity. ### 🌬 What is the Middle Ear Cleft? The **Middle Ear Cleft** is a continuous air-filled space within the temporal bone, comprised of: 1. The **Tympanic Cavity** (Middle Ear Cavity) 2. The **Eustachian Tube** 3. The **Mastoid Air Cell System** The Tympanic Cavity is the irregular space located between the **Tympanic Membrane** laterally and the **Osseous Labyrinth** (Inner Ear) medially. --- ### 👂 The Middle Ear Cavity The middle ear cavity is an irregular shape. Due to the **convexity** of the medial wall (promontory) and the **concavity** of the lateral wall (tympanic membrane), it is **constricted in the center**. - **Width**: - ~2 mm at the center (at the umbo) - ~6 mm superiorly (in the attic/epitympanum) - ~4 mm inferiorly (in the hypotympanum) - Widest in the attic, thinnest at the center. - **Vertical & Anterior-Posterior Length**: ~15 mm - **Volume**: 1-2 cm³ of air. A minimum volume of 0.5 cm³ is necessary for normal function. #### 🧭 **Relations of the Middle Ear Cavity:** The middle ear cavity has six "walls" with important relations: - **Superior**: Middle Cranial Fossa and Temporal Lobe. - **Inferior**: Jugular Bulb (posteriorly) and Internal Carotid Artery (anteriorly). - **Lateral**: Tympanic Membrane (separating it from the External Auditory Meatus). - **Medial**: Inner Ear (Osseous Labyrinth). - **Anterior**: Openings related to the Tensor Tympani muscle and Eustachian Tube. - **Posterior**: Mastoid Air Cell System (communicates with the Mastoid Antrum via the Aditus ad Antrum). ### ✨ Parts of the Middle Ear Cavity The middle ear cavity can be divided into three main portions: 1- **Mesotympanum**: The part lying opposite the **Pars Tensa** of the Tympanic Membrane. - _**Contents**_: Stapes, long process of Incus, Oval Window, Round Window. - Eustachian tube exits from its anterior aspect (Protympanum). - Posterior wall contains **Facial Recess** and **Sinus Tympani**. >What are the boundaries of **Facial Recess**? >What are the boundaries of **Sinus Tympani**? 2- **Epitympanum (Attic)**: The portion **above the level of the short/lateral process of the Malleus**. Lies within the notch of Rivinus (dehiscence in the tympanic bone). - *Lateral Boundary*: Pars Flaccida and the Bony Outer Attic Wall. - _**Contents**_: Head of the Malleus, Body of the Incus, associated ligaments and mucosal folds. >What is **Cog**? 3- **Hypotympanum**: The lowest portion, lying **below the level of the inferior part of the Tympanic Sulcus** (or bony ear canal). - Floor is related to the Internal Jugular Vein and Internal Carotid Artery. 4- **Protympanum**: The portion of the middle ear around the tympanic orifice of the **Eustachian Tube**, located in the anterior wall. --- ### 🧱 Anatomy of the Middle Ear Walls The middle ear cavity has six walls: **1. Lateral Wall** - Partly bony, partly membranous. - Formed by: - Bony lateral wall of the Epitympanum superiorly (part of the squamous bone). - Tympanic Membrane centrally. - Bony lateral wall of the Hypotympanum inferiorly. >What is **Scutum**? What is it's clinical importance? >What are the boundaries of **Prussak's space**? - **Openings (Tympanic Canaliculi)**: - Petrotympanic Fissure - Canal of Huguier - Posterior Canaliculus (for Chorda Tympani) >What is the other name of **Petrotympanic Fissure**? What structures pass through it? >Which nerve passes through **Canal of Huguier**? **2. Floor (Inferior Wall)** - Very narrow. - Thin plate of bone separating the middle ear from the **Jugular Bulb** (posteriorly) and **Internal Carotid Artery** (anteriorly). - **Inferior Tympanic Canaliculus**: Small canal near the fossula petrosa (between jugular bulb fossa and carotid canal). Houses the inferior ganglion of the glossopharyngeal nerve. >What structures pass through the **Inferior Tympanic Canaliculus**? - _**Clinical Importance**_: - Dehiscence - High-riding Jugular Bulb **3. Posterior Wall** - The highest wall (~14 mm), formed by petrous bone. Wider superiorly. - Separates middle ear from mastoid air cells, *except* at the Aditus ad Antrum. - **Aditus ad Antrum**: Triangular communication (~4x4x4 mm) between the **Epitympanum** (anteriorly) and the **Mastoid Antrum** (posteriorly). - Divisions: Upper 1/3 (corresponds to Aditus ad Antrum), Lower 2/3 (Retrotympanum). >What is **Incudal Buttress**? >What is **Incudal Fossa** and what structure is present in it? - Lower 2/3: Bony wall from bony annulus to labyrinth. Houses the vertical segment of the **Facial Nerve**, Styloid eminence, Pyramidal eminence, Fossa Incudis. - _**Note**_: The lower posterior wall presents structures dividing the retrotympanum into spaces: - **3 Eminences**: Pyramidal, Caudal, Styloid. - **7 Bony Ridges**: Caudal, Pyramidal, Styloid, Ponticulus, Subiculum, Fustis, Funiculus. - **4 Sinuses/Spaces**: Facial Sinus, Lateral Tympanic Sinus (Lateral); Posterior Tympanic Sinus, Sinus Tympani (Medial). >To know more about the eminences, Bony ridges and sinuses in the posterior wall of Middle ear, get access to my full notes by purchasing it. >What is Subiculum? >What structure is present in the Pyramidal eminence? >What is Ponticulus? What are it's 2 variations? **4. Anterior Wall** - Separates middle ear cavity from the **Petrous Carotid Canal** (Internal Carotid Artery). - Narrow as medial/lateral walls converge anteriorly. - Divisions: - **Lower Portion**: Largest, anterior wall of Hypotympanum. Thin bone separating middle ear from vertical segment of carotid artery. Contains two tiny openings for **Caroticotympanic nerves** (superior/inferior) transmitting sympathetic fibers from the carotid sympathetic chain to the tympanic plexus on the promontory. - **Middle Portion (Protympanum)**: Contains two tunnels (separated by the **Septum Canalis Musculotuberius**). - Upper tunnel: Transmits the **Tensor Tympani muscle**. - Lower tunnel: Bony portion of the **Eustachian Tube**. - **Upper Portion**: Root of the Zygoma, forms the anterior wall of the Epitympanum. **5. Medial Wall (Labyrinthine Wall)** - Separates the middle ear from the **Inner Ear**. - Important Structures: **Cochlear Promontory**, Tympanic segment of **Facial Nerve**, **Oval Window**, **Round Window**, Tensor Tympani canal, **Cochleariform Process**, Lateral Semicircular Canal. - Divisions (using Tensor Tympani canal and Facial Nerve as landmarks): - Upper 1/3: Medial wall of the **Epitympanum**. Demarcated posteriorly by the Lateral Semicircular Canal. - Lower 2/3: Medial wall of the **Mesotympanum**. Contains the Cochlear Promontory, Oval Window, and Round Window. >Which nerve plexus is found on the Cochlear Promontory? What nerves contribute to it? - **Facial Nerve Canal (Tympanic Segment)**: Runs obliquely posterior-superiorly above the oval window. Joins the vertical segment at the **Second Genu**. - **Oval Window (Fossa Vestibuli)**: Situated posterior and superior to the promontory. Closed by the **Stapes Footplate** surrounded by the **Annular Ligament**. - **Round Window**: Situated posterior and inferior to the promontory. Covered by the **Round Window Membrane**. - **Tensor Tympani Bony Canal**: Tensor Tympani semicanal runs from protympanum, ends just anterior to oval window niche. - **Lateral Semicircular Canal**: Above the level of the facial nerve canal, forms the medial wall of the **Attic**. >What is the **Cochleariform Process** ? What structure passes through it? #### 6. Superior Wall (Roof) - Formed by a thin plate of bone called the **Tegmen Tympani**. - Separates the middle ear cavity from the overlying **Middle Cranial Fossa**, **Dura**, and **Temporal Lobe**. - Parts: - **Tegmen Tubae**: Overlying the Eustachian tube. - **Tegmen Tympani**: Overlying the Tympanic Cavity. - **Tegmen Antri**: Overlying the Mastoid Antrum. - Superior surface is covered by dura, inferior surface by middle ear mucosa. Separates CSF from air space. - Formed by the tegmental plate of the petrous bone and the horizontal plate of the squamous bone. - **Petrosquamous Suture**: Between petrous and squamous parts. Unossified in newborns, closes in adulthood. Dura can be tightly adherent here. --- ## About This Note This free ENT note on Anatomy of Middle Ear - Walls & Parts was written by Dr. Mausumi Das and is paired with a corresponding video lecture. 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