Rhinology Selections, Lecture notes of Human Biology

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Selected Rhinology works of

Balasubramanian Thiagarajan

From the SelectedWorks of Balasubramanian

hiagarajan

September 2012

Advanced anatomy of lateral nasal wall For the

endoscopic sinus surgeon

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ethmodial complex where as the inferior turbinate is a separate bone. Commonly a prominence may be seen at the attachment of the middle turbinate.

lateral wall of nose after removal of turbinates

This prominence is known as the agger nasi cell. This prominence varies in size in different individuals. These agger nasi cells overlie the lacrimal sac, separated from it just by a thin layer of bone. Infact this agger nasi cell is considered to be a remnant of naso turbinal bones seen in animals. When the anterior attachment of the inferior and middle turbinates are removed, the lacrimal drainage system and sinus drainage system can be clearly seen. The inferior turbinate is a separate bone developed embryologically from the maxilloturbinal bone. The inferior meatus is present between the inferior turbianate and the lateral nasal wall. The nasal opening of the naso lacrimal duct opens in the anterior third of the inferior meatus. This opening is covered by a mucosal valve known as the Hassner’s valve. The course of the naso lacrimal duct from the lacrimal sac lie under the agger nasi cell. The middle meatus lie between the middle turbinate and the lateral nasal wall. The middle turbinate is part of the ethmoidal complex. The sinuses have been divided into the anterior and posterior groups. The anterior group of sinuses are frontal, maxillary and anterior ethmoidal sinuses. These sinuses drain into the middle meatus, i.e. under the middle turbinate. The middle meatus hosts from anterior to posterior the following structures:

1. Agger nasi
2. Uncinate process
3. Hiatus semilunaris
4. Ethmoidal bulla
5. Sinus lateralis
6. Posterior fontanelle Uncinate process: actually forms the first layer or lamella of the middle meatus. This is the most stable landmark in the lateral nasal wall. It is a wing or boomerang shaped piece of bone. It attaches anteriorly to the posterior edge of the lacrimal bone, and inferiorly to the superior edge of the inferior turbinate. Superior attachment of the uncinate process is highly variable, may be attached to the lamina palyracea, or the roof of the ethmoid sinus, or sometimes to the middle turbinate. The configuration of the ethmoidal infundibulum and its relationship to the frontal recess depends largely

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on the behavior of the uncinate process. The Uncinate process can be classified into 3 types depending on its superior attachment. The anterior insertion of the uncinate process cannot be identified clearly because it is covered with mucosa which is continuous with that of the lateral nasal wall. Sometimes a small groove is visible over the area where the uncinate attaches itself to the lateral nasal wall. The anterior convex part forms the anterior boundary of the ostiomeatal complex. It is here the maxillary, anterior ethmoidal and frontal sinuses drain. Uncinate process can be displaced medially by the presence of polypoidal tissue, or laterally against the orbit in individuals with maxillary sinus hypoplasia. Removing of this piece of bone is the most important step in Endoscopic sinus surgery. Type I uncinate: Here the uncinate process bends laterally in its upper most portion and inserts into the lamina papyracea. Here the ethmoidal infundibulum is closed superiorly by a blind pouch called the recessus terminalis (terminal recess). In this case the ethmoidal infundibulum and the frontal recess are separated from each other so that the frontal recess opens into the middle meatus medial to the ethmoidal infundibulum, between the uncinate process and the middle turbinate. The route of drainage and ventilation of the frontal sinus run medial to the ethmoidal infundibulum.

Type I uncinate insertion

Type II uncinate: Here the uncinate process extends superiorly to the roof of the ethmoid. The frontal sinus opens directly into the ethmoidal infundibulum. In these cases a disease in the frontal recess may spread to involve the ethmoidal infundibulum and the maxillary sinus secondarily. Sometimes the superior end of the uncinate process may get divided into three branches one getting attached to the roof of the ethmoid, one getting attached to the lamina papyracea, and the last getting attached to the middle turbinate.

Type II uncinate insertion

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Hypoplasia of maxillary sinus seen pushing the uncinate laterally

Image showing uncinate process

Removal of uncinate process reveals the natural ostium of the maxillary sinus. This is another vital landmark in the lateral nasal cavity. The superior wall of the natural ostium of the maxillary sinus is at the level of floor of the orbit.Agger nasi: This is a latin word for “Mound”. This area refers to the most superior remnant of the first ethmoturbinal which presents as a mound anterior and superior to the insertion of middle turbinate.Depending on the pneumatization of this area may reach up to the level of lacrimal fossa thereby causing narrowing of frontal sinus outflow tract. Ethmoidal infundibulum: is a cleft like space, which is three dimensional in the lateral wall of the nose. This structure belongs to the anterior ethmoid. This space is bounded medially by the uncinate process and the mucosa covering it. Major portion of its lateral wall is bounded by the lamina papyracea, and the frontal process of maxilla to a lesser extent. Defects in the medial wall of the infundibulum is covered with dense connective tissue and periosteum. These defects are known as anterior and poterior fontanelles. Anteriorly the ethmoidal infundibulum ends blindly in an acute angle.

Figure showing large agger nasi air cell

Bulla ethmoidalis: This is derived from Latin. Bulla means a hollow thin walled bony prominence. This

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is another landmark since it is the largest and non variant of the aircells belonging to the anterior ethmoidal complex. This aircell is formed by pneumatization of bulla lamella (second ethmoid basal lamella). This air cell appears like a bleb situated in the lamina papyracea. Some authors consider this to be a middle ethmoid cell. If bulla extends up to the roof of ethmoid it can form the posterior wall of frontal recess. If it does not reach up to the level of skull base then a recess can be formed between the bulla and skull base. This recess is known as suprabullar recess. If the posterior wall of bulla is not in contact with basal lamella then a recess is formed between bulla and basal lamella. This recess is known as retrobullar recess / sinus lateralis. This retrobullar recess may communicate with the suprabullar recess. Osteomeatal complex: This term is used by the surgeon to indicate the area bounded by the middle turbinate medially, the lamina papyracea laterally, and the basal lamella superiorly and posteriorly. The inferior and anterior borders of the osteomeatal complex are open. The contents of this space are the aggernasi, nasofrontal recess (frontal recess), infundibulum, bulla ethmoidalis and the anterior group of ethmoidal air cells.This is infact a narrow anatomical region consisting of : 1. Multiple bony structures (Middle turbinate, uncinate process, Bulla ethmoidalis) 2. Air spaces (Frontal recess, ethmoidal infundibulum, middle meatus) 3. Ostia of anterior ethmoidal, maxillary and frontal sinuses. In this area, the mucosal surfaces are very close, sometimes even in contact causing secretions to accumulate. The cilia by their sweeping movements pushes the nasal secretions. If the mucosa lining this area becomes inflamed and swollen the mucociliary clearance is inhibited, eventually blocking the sinuses. Some authors divide this osteomeatal complex into anterior and posterior. The classic osteomeatal complex described already has been described as the anterior osteomeatal complex, while the space behind the basal lamella containing the posterior ethmoidal cells is referred to as the posterior ethmoidal complex, thus recognising the importance of basal lamella as an anatomical landmark to the posterior ethmoidal system. Hence the anterior and the posterior osteomeatal complex has separate drainage systems. So when the disease is limited to the anterior compartment of the osteomeatal complex, the ethmoid cells can be opened and diseased tissue removed as far as the basal lamella, leaving the basal lamella undisturbed minimising the risk during surgery.Hiatus semilunaris: Lies between the anterior wall of the Bulla and the free posterior margin of the uncinate process. This is infact a two dimensional space. Through this hiatus a cleft like space can be entered. This is known as the ehtmoidal infundibulum. This ethmoidal infundibulum is bounded medially along its entire length by the uncinate process and its lining mucosa. The lateral wall is formed by the lamina papyracea of the orbit, with participation from the frontal process of the maxilla and the lacrimal bone. The anterior group of sinuses drain into this area. Infact this area acts as a cess pool for all the secretions from the anterior group of sinuses.

Osteomeatal complex

Concha bullosa: Sometimes middle turbinate may become pneumatized. This pneumatization is known

From the SelectedWorks of Balasubramanian

hiagarajan

February 2013

Anatomy of Orbit Otolaryngologist's perspective

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Anatomy of Orbit Otolaryngologist's perspective February 9, 2013 · Rhinology

A careful study of anatomy of orbit is very important to an ENT surgeon because of its proximity to the para nasal sinuses. A comprehensive knowlege of orbital and peri orbital anatomy is necessary to understand the various disorders of this region and in its surgical mangement. Current day otolaryngologists venture into other unchartered territories like orbit, lacrimal sac etc. Anatomical knowledge of this area will help otolaryngologists to avoid complications during surgical procedures involving this area. This article attempts to explore this topic from otolaryngologist’s perspective.

Introduction: Orbit supports the eye and ensures that this organ functions in an optimal manner. It also protects this vital structure. The shape of the orbit resembles a four sided pyramid to begin with but as one goes posterior it becomes three sided towards the apex. The volume of the orbital cavity in an adult is roughly about 30cc. The rim of orbit in an adult measures about 40mm horizontally and 35 mm vertically. The medial walls of orbit are roughly parallel and are about 25 mm apart in an adult. The lateral walls of orbit angles about 90 degrees from each other. This is actually a fixed cavity with no scope for enlargement, hence a small increase in ocular pressure can lead to disastrous consequences. Osteology: Seven bones join together to form the orbit. These include:

1. Frontal bone
2. Lacrimal bone
3. Zygoma
4. Maxilla
5. Ethmoid
6. Sphenoid
7. Palate The orbital rim is more or less spiral with its two ends overlapping medially on either side of lacrimal fossa. The inferior orbital rim is formed by the maxillary bone medially and zygomatic bone laterally. The zygomatic bone forms the lateral orbital rim, while the frontal bone forms the superior orbital rim.

Abstract

Anatomy of orbit

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Author Professor Balasubramanian Thiagarajan Balasubramanian Thiagarajan

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mucosa and duramater of frontal bone area. The cranial opening of these ethmoidal canals are related to the anterior and posterior limits of cribriform plate. The roof of the nasal cavity is partially formed by the cribriform plate of ethmoid. These cranial openings of ethmoidal canals divide anterior skull base into frontal, cribriform, and planum areas. Ethmoidal canals divide orbit into bulbar, retrobulbar and apical portions. This intricate knowledge of orbital anatomy helps during advanced endoscopic skull base surgical procedures. The medial wall of the orbit is formed from anterior to posterior by :

1. frontal process of maxilla
2. lacrimal bone
3. ethmoid bone
4. lesser wing of sphenoid bone The thinnest portion of the medial wall is the lamina papyracea which separates the ethmoidal sinuses from the orbit. It is one of the components of ethmoid bone. Infections from ethmoidal sinus can easily breach this paper thin bone and affect the orbital contents. The medial wall of the orbit is thicker posterior where the sphenoid bone is present and anteriorly where the posterior lacrimal crest is present. The fronto ethmoidal suture line marks the approximate level of ethmoidal sinus roof, hence any dissestion above this line may expose the cranial cavity. The anterior and posterior ethmoidal foramina through which branches of ophthalmic artery (anterior and posterior ethmoidal arteries) and branches of naso ciliary nerve passes are present in this suture. The anterior ethmoidal foramen is located at a distance of 24 mm from the anterior lacrimal crest, while the posterior ethmoidal foramen is located at a distance of 36 mm from the anterior lacrimal crest. A vertical suture that runs between the anterior and posterior lacrimal crests is the anastomotic area between the maxillary and the lacrimal bone. If this suture is located more anteriorly it indicates a predominance of lacrimal bone, while a more posteriorly placed suture line indicates a predominance of maxillary bone in the anastomotic relationship. The lacrimal bone at the level of lacrimal fossa is pretty thin (106 micrometer). This bone can be easily penetrated during dacryocystorhinostomy surgery. If the maxillary component is predominant it becomes difficult to perform the osteotomy in this area to access the sac because the maxillary bone is pretty thick. Hence lacrimal bone predominance makes it easy to expose the sac during dacryocystorhinostomy. Applied anatomy of medial wall of orbit: This wall is aligned parallel to the antero posterior axis and is very fragile because of its proximity to anterior ethmoidal air cells. Disruption of this wall due to trauma causes hypertelorism (Traumatic Hypertelorism). Lateral displacement of frontal process of maxilla will cause traumatic telecanthus because the medial palpebral ligament is attached here. Both hypertelorism and telecanthus can be caused due to trauma. Contribution of ethmoid bone: Ethmoid bone forms the medial boundary of orbit. It is separated from obital contents by a paper thin bone (Lamina papyracea). This bone can be breached due to diseases involving ethmoids or during nasal surgeries allowing infections to reach the orbital cavity. Inferiorly ethmoid bone articulates with the orbital plate of maxilla. Posteriorly the ethmoid bone articulates with the body of sphenoid

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completing the medial bony wall of orbital cavity. Sphenoid bone: Sphenoid bone contributes to the formation of bony orbit by its greater and lesser wings. The lesser wings of sphenoid articulates with orbital plate of frontal bone to form the roof of orbit. The greater wings of sphenoid articulates laterally with the orbital plate of zygoma forming the lateral wall of bony orbit. Lateral wall of orbit: Understanding this wall of the orbit is vital from the surgeon’s point of view. Two components are involved in the formation of this wall. The greater wing of sphenoid faces the orbit on its exocranial side and its endocranial surface forms the anterior limit of middle cranial fossa. The zygomatic bone on the contrary does not have cerebral surface / endocranial surface. It virtually faces the orbit while its opposite surface froms the anterior limit of infratemporal fossa. This anatomical relationship provides lateral access to the orbit without resorting to craniotomy. In the lateral orbital approach, the contents of the orbit can be reached just by displacing the temporal bone and performing zygomatic osteotomy. The recurrent meningeal branch of middle meningeal artery may be seen coursing through a foramen in the suture line between the frontal and sphenoid bones. This artery forms a anastomosis between the external and internal carotid arterial systems. Roughly 4 – 5 mm behind the lateral orbital rim and 1 cm inferior to the frontozygomatic suture is the lateral tubercle of Whitnall. The following structures gets attached to this tubercle:

1. Lateral canthal tendon
2. Lateral rectus check ligament
3. Suspensory ligament of lower eyelid (Lockwoods ligament).
4. Orbital septum
5. Lacrimal gland fascia. Lateral canthal tendon: The pretarsal muscles join laterally to form the lateral canthal tendon. This tendon inserts into the periosteum of Whitnall’s tubercle about 5 mm behind the infraorbital rim. Lateral rectus check ligament: This is a fibrous membrane arising from the lateral rectus muscle and gets attached to the zygomatic tubercle, posterior aspect of lateral palpebral ligament and the lateral conjunctival fornix. Being most prone for injury this wall of the orbit happens to be the thickest. It is very strong at the orbital margin. Behind this thick portion of lateral wall comes the somewhat thinner portion, behind this thin portion the wall again becomes thick. Posterior most portion of this lateral wall is thin (about 1 mm) nearly translucent. This wall is further weakend by the presence of superior orbital fissure between lateral and superior walls of orbit. The presence of inferior orbital fissure between lateral and inferior walls of orbit creates another area of weakness.

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Lockwood’s ligament: This ligament acts as a hammock supporting the globe inferiorly. This is actually a dense condensation of connective tissue engulfing inferior rectus and inferior oblique muscles providing support to the undersurface of the globe. This ligament is attached to facial structures connected to the lower lid. Damage to Lockwood’s ligament can cause lower eyelid ptosis which is seen in patients

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undergoing total maxillectomy.

Figure showing Lockwood’s ligament acting as a Hammock holding the globe

Orbital septum: This is also known as palpebral ligament. This membranous sheet acts as the anterior boundary of the orbit. It extends from the orbital rims to the eyelids. With age this septum may weaken causing prolapse of orbital fat forwards. Blepharoplasty is usually performed to correct this anamoly. Orbital septum helps in differentiating orbital cellulitis (behind the septum) and periorbital cellulitis (in front of the septum). This structure is usually penetrated by vessels and nerves that pass from the orbit to face and scalp. The frontal process of zygomatic bone and the zygomatic process of frontal bone are thick and they protect the globe from lateral trauma. Just behind this facial buttress area the posterior zygomatic bone and the orbital plate of greater wing of sphenoid are thinner thus making the zygomatico sphenoid suture a convenient land mark for lateral orbitotomy. The zygomatico facial and zygomatico temporal nerves and vessels pass through the lateral wall of the orbit to reach the cheek and temporal regions. Posteriorly the lateral wall thickens and meets the temporal bone which forms the lateral wall of the cranial cavity. When lateral orbitotomy is being done only 12 – 13 mm separate the posterior aspect of lateral orbitotomy to that of the middle cranial fossa. This distance could still be shorter in females. Foramen and fissures of orbit: The following are the various foramina and fissures of orbit:

1. Superior orbital fissure (sphenoidal fissure)
2. Inferior orbital fissure (sphenomaxillary fissure)
3. Anterior and posterior ethmoidal canals
4. Optic canal/foramen

Orbit showing various components

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posteriorly. This is actually not horizontal, but slopes upwards and medially at an angle of 45°. It ends as the anterior margin of inferior orbital fissure. In this area this bone abruptly curves downwards towards the infratemporal fossa forming the posterior wall of maxilla. Components of the floor of the orbit:

1. Orbital plate of maxilla (largest component)
2. Orbital plate of zygomatic bone (antero lateral part)
3. Orbital process of palatine bone (forms a small portion behind the maxilla) The floor of the orbit is traversed by inferior orbital fissure. This fissure infact weakens the floor. Most of blowout fractures occur medial to this fissure. Fracture line can cause entrapment of infraorbital nerve leading on to anesthesia of cheek area of that side. Infraorbital canal formed from this fissure sinks anteriorly and opens into the infraorbital foramen. The roof of the orbit slopes down medially. In fact this slope continues up to fronto ethmoidal suture to form the roof of the ethmoid sinus. This is otherwise known as fovea ethmoidalis. The anatomical relationship between the anterior ethmoidal air cells and the lacrimal fossa should be borne in mind to avoid confusion between the ethmoid and nasal cavities during dacryocystorhinostomy surgery. Ethmoidal foramen: These foramina lie between the roof and medial wall of orbit. These foramina invariably lie within the frontoethmoidal suture line or in the frontal bone. These openings form canals known as anterior and posterior ethmoidal canals. These canals are formed by frontal bone to a great extent with minor contributions from ethmoids. Anterior ethmoidal canal: This canal is directed backwards and laterally. This foramen is located about 24 mm from the anterior lacrimal crest. The posterior border of this canal is not well defined and is continuous with a groove on the orbital plate of ethmoid. This canal opens into the anterior cranial fossa at the side of cribriform plate transmitting anterior ethmoidal nerve and artery.

Figure showing anterior ethmoidal artery

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Posterior ethmoidal canal: This canal lie posterior to anterior ethmoidal canal. This foramen is located 36 mm from the anterior lacrimal crest. It transmits posterior ethmoidal nerve and posterior ethmoidal artery. Optic foramen: Also known as optic canal. It begins from the middle cranial fossa and extends up to the apex of the orbit. This foramen is formed by two roots of the lesser wing of sphenoid. This foramen is directed laterally, forwards and downwards. This canal is funnel shaped, the mouth of the funnel is its anterior opening. This foramen is oval in shape with the vertical diameter being the greatest. Its intracranial opening is flattend above downwards, where as its middle portion is circular in nature. Its lateral border is well defined and is formed by the anterior border of the posterior root of lesser wing of sphenoid. Its medial border is less well defined. Optic canal is separated from the medial end of superior orbital fissure by a bar of bone. This bar of bone has a tubercle for the attachment of annulus tendinous.

Diagram showing view of skull after removal of lateral wall

Optic nerve canal transmits:

1. Optic nerve
2. Coverings of optic nerve including duramater, arachnoidmater and piamater.
3. Opthalmic artery lies below and lateral to the nerve embedded in the dural sheath Orbital index:

The width of the orbit is larger than that of its height. Orbital index varies among various human races. Going by orbital index 3 types of orbits have been identified. Orbital index= height of the orbit _______________ X 100 Width of the orbit Megaseme: This is a rather large orbital index. Here the orbital index calculated using the formula above is more than 89. This orbit is the classic feature of yellow races.