 Our new topic is Orofacial and neck infections. This lecture is intended to introduce you to the facial layers of the neck which is also called as cervical fascia. First you should understand what the term fascia means. Fascia is a band or sheet of connective tissue primarily of collagen and it is found beneath the skin. And what are its functions? The fascia attaches, stabilizes, encloses and separates the muscles and other internal organs. There is one more term that you need to be familiar with that is facial space. These are potential spaces that exist between the fascia and underlying organs and other tissues. And they are separated from each other by barriers which may be a muscle, a bone or fascia. A neurontogenic infection can reach these facial spaces resulting in space infection. Generally the spread of infection is determined based on whether the anatomical barrier. It can be a muscle, bone or fascia. So it depends on the anatomical barrier whether it is breached or not. What is the significance of these facial spaces or space infection? Space infections are relatively common sequelae of odontogenic infection and rapidly progressing which results in prolonged morbidity. There are long term complications associated with space infections which are potentially life threatening. The treatment of space infections are also considerable difficult due to various factors like the complexity of the anatomy of neck, the deeper location of the spaces, limited access, proximity to vital structures and communication of spaces with each other. So that said let's have a look at the cervical fascia in detail. Cervical fascia is divided into superficial cervical fascia and deep cervical fascia. Superficial cervical fascia is a thin layer of subcutaneous connective tissue that lies between the dermis of the skin and the first layer of deep cervical fascia which is the investing layer. It contains the following. The neurovascular supply to the skin, superficial veins and lymph nodes, fat and platysma muscle. Superficial cervical fascia is thinner on the anterior aspect of the neck and it has usually got very thin amount of fat which is its distinguishing characteristic. At the anterior neck the superficial fascia blends with the platysma. Platysma is a broad superficial muscle which originates from the fascia over the pectoralis major and deltoid. The fibers of platysma then causes the clavicle and meat in the midline fusing with the muscles of the face. It is beneath the superficial cervical fascia that you can find the external jugular vein. Beneath the superficial cervical fascia you find the deep cervical fascia. The deep cervical fascia as its name suggests lies deep to the superficial cervical fascia and the platysma muscle. This fascia is organized into several layers and each of these layers have role in supporting the neck structures. We shall now have a look at each of these layers in detail. From here onwards you will see the same diagram in every following slide throughout this presentation because this is the best way to visualize and compare the facial layers at a glance. Before looking into the diagram let us understand that any object or human body can be visualized in three different planes the sagittal, coronal and transverse planes. The sagittal plane divides the human body into equal right and left halves through the midline. The sagittal plane is shown in right color here. The coronal plane divides the human body into anterior and posterior halves or anterior and posterior parts. Transverse plane also called the axial plane or cross sectional plane divides the body into inferior and superior portion. So this is applicable to human body as well as any object. So keep this image in mind while discussing the topic proper images. This figure shows the cross sectional image of neck at the level of seventh cervical vertebra of the C7. You have sectioned the neck at the level of C7 and you are viewing it from above. This is a superior view. So let's see what all structures you can identify here. Because this is sectioned at C7 level here is the seventh vertebra and through the center runs the spinal cord this is the spinal cord this is the C7 vertebra. So to identify the structures let's move from anterior to posterior this is the anterior aspect this is the posterior aspect. So anteriorly you can visualize the superficial cervical fascia with the platysma. This muscle is the platysma the thin muscle over here is the platysma and around it you have the superficial cervical fascia. You know from the previous slide that platysma is the limit of superficial cervical fascia. With the platysma you can identify the external jugular vein. The deep cervical fascia begins at the investing layer which is shown in green color. So investing layer surrounds the entire neck as you can see very clearly here the investing layer which is green in color surrounds the entire cross section of the neck. You can see the sternocleidomastoid muscle on either side and also the smaller infrahiroid muscles. These are the infrahiroid muscles the ones smaller in size. As you move further deeper the structure in pink here is the thyroid. This overlies the crachia which is blue in color this is thyroid this is crachia and the structure behind the crachia in red color is the esophages. So the thyroid the crachia and esophages are enclosed within the second layer of deep cervical fascia which is the pre tracheal layer that is illustrated in blue color here. As you still go posteriorly there is carotid sheath which is red in color on either side and the carotid sheath encloses the common carotid artery the internal jugular vein and the vagus nerve. Orange colored layer here is the pre vertebral fascia. There are different groups of muscles around the cervical vertebra which is enclosed by the pre vertebral fascia and most posteriorly you can see that the investing layer of deep cervical fascia has split itself to enclose the trapezius muscle. So this is the description of deep cervical fascia in a nutshell. Moving on to the investing layer of deep cervical fascia which is depicted in blue color here. It is the most superficial aspect of the deep cervical fascia and is clearly seen in the diagram here that it surrounds all the structures in the neck like a collar. Here again is a cross sectional view of the neck at C7 level. This is the anterior part here is the posterior part and where the investing fascia meets the trapezius muscle and the sternocleidomastoid muscle it splits into two and it completely surrounds both the muscles. So imagine the investing fascia as a tube with superior, inferior, anterior and posterior attachments. In the cross sectional image you cannot see the superior and inferior limits therefore here is the sagittal view. The green color here is the investing fascia. Similarly it is attached to the external occipital protuberance, the superior nuclei of the skull, the mastoid process and the base of the mandible that is the superior limit and anteriorly the limit is the hyoid bone and the symphysis mentee. It is attached along the nuke line of the vertebral column and the spine of C7, it is attached to the ligamentum nuke and the spine of seventh cervical vertebra. Inferiorly the limit is the manupremia sternum. So these are the attachments of investing layer of deep cervical fascia. It is like the investing fascia splits to enclose two muscles that is the sternocleidomastoid muscle and the trapezius muscle. Similarly the fascia also splits to enclose two glands, those are the submandibular and submental glands and two spaces the suprasternal and supraclavicular spaces. So these are the structures or the regions surrounded by or enclosed by the investing layer of deep cervical fascia. The second layer or the pre-tracheal layer of deep cervical fascia. In the sagittal view here the pre-tracheal layer is depicted in blue color. This is situated in the anterior neck and it extends between the hyoid bone and the oblique line of thyroid cartilage superiorly and trax inferiorly where it blends with the pedicardium of the arch of the iota. In the cross sectional image the pre-tracheal layer fuses with the cadouted sheath deep to the sternocleidomastoid muscle. So here is the cadouted sheath to which the pre-tracheal layer is blended on either side. So here in this diagram you can see that the pre-tracheal layer has enclosed few muscles over here. These are the infrahioid muscles. It has also enclosed the thyroid gland, the trachea and the esophages. So anatomically pre-tracheal fascia can be divided into two parts. The muscular part and the visceral part. The muscular part encloses the infrahioid muscles and the visceral part encloses the thyroid trachea and the esophagus. There are few other features of the pre-tracheal layer. On either side of the thyroid gland it forms a suspensory ligament for the gland which is known as the ligament of berry. This ligament is attached to the cricoid cartilage and also to the thyroid cartilage. So its function is to support the thyroid gland and the thyroid doesn't sink into the medial stenum. This fascia also provides a slippery surface for the free movement of the trachea during swallowing. Moving on to the pre-vertibule layer. As the name suggests it lies in front of the pre-vertibule muscles and forms the flow of the posterior triangle of the neck. As you can see here the purple coloured is the pre-vertibule fascia and the pre-vertibule muscles lie between the fascia and the vertebra which is coloured in pink. There are three sets of muscles associated with this fascia. The first group of muscles is located anterior to the vertebrae and it includes the longest capitals and longest scaly muscles. The second group of muscles is the scalenes muscles which include the anterior, middle and posterior scalenes as well as the levator scapulae which is located lacquely to the vertebra. And posteriorly the deep muscles or influencing muscles of the back are located. The sagittal section shows the pre-vertibule fascia in brown colour. Superiorly it is attached to the skull base and inferiorly it extends to the superficial mediasenium where it is attached to the body of the fourth thoracic vertebra. And anteriorly the pre-vertibule fascia is separated from the pharynx and buccopharyngeal fascia by the retropharyngeal space containing loose areola tissues. This is the sagittal view and here is the cross-sectional view of the same region. The pre-vertibule fascia is illustrated in blue colour and the orange colour shows the retropharyngeal space. Anterior to the retropharyngeal space is the buccopharyngeal fascia. So this space differentiates or separates the buccopharyngeal fascia from the pre-vertibule fascia. This region is of utmost importance in dealing with or while dealing with space infections. The importance of this region will be dealt in detail in the subsequent lectures. The next layer of deep cervical fascia is the carotid sheet. It is paired and present on either side of the neck. The carotid sheet encloses the internal jugular vein, the common carotid artery and the vagus nerve. In addition, it has relations to ansa cervicalis anteriorly and the cervical sympathetic chain posteriorly. The carotid sheet is formed by the fusion of pre-tracheal, investing layer and the pre-vertibule layers of deep cervical fascia. It is within this carotid sheet that the common carotid artery bifurcates into the internal and external carotid artery. It is only the internal carotid artery that is present within the sheet. The same diagram is depicted here. This is the internal jugular vein, the common carotid artery, the ansa cervicalis and the sympathetic trunk. As you can see here, the carotid sheet is organised into a column. So the superior limit of the sheet is the base of the skull and the inferior limit is the thoracic mediasthenum. And this particular organisation is of clinical significance as a pathway for the spread of infection. Bacopharyngeal fascia wraps around the lateral and posterior sides of the pharynx and it lies on the superficial side of the pharyngeal constrictor muscle. It was told earlier that the pre-vertibule fascia is separated from the bacopharyngeal fascia by the retropharyngeal space. Again there is aller fascia which is red in colour which is present between the retropharyngeal space and the pre-vertibule fascia. As you can see here, the red coloured structure is the aller fascia which lies just posterior to the retropharyngeal space. So these structures will prevent the meeting or communication between the two fascias that is the pre-vertibule fascia and the bacopharyngeal fascia. But there is one point where the aller fascia fuses with the retropharyngeal space. As you can see here at this particular point the aller fascia and the retropharyngeal space or it is retropharyngeal fascia as you can call it either way. So at this point both the fascias meet and here ends the retropharyngeal space. So it is probably at this level that the pre-vertibule fascia communicates with the bacopharyngeal fascia as you can see in this diagram. Here is the midline fusion between the pre-vertibule fascia and the bacopharyngeal fascia which is at a variable level between the sixth cervical vertebrae that is C6 and the fourth thoracic vertebrae T4. So this meeting point of the pre-vertibule fascia and the bacopharyngeal fascia is somewhere between C6 and T4. Faryngeal basilar fascia is a thickened part of the deep cervical fascia between the upper border of the superior constrictor muscle and the base of the skull. This lies deep to the pharyngeal muscles. This figure again depicts the relationship between the pre-vertibule fascia, the bacopharyngeal fascia and the pharyngeal basilar fascia. The dark blue color is the pre-vertibule fascia, the light blue is the bacopharyngeal fascia which will eventually meet somewhere between C6 and T4. Between the pharyngeal basilar and the bacopharyngeal fascia lies the constrictor muscles of the pharynx. So this is how all the three fascia, the bacopharyngeal pharyngeal basilar and pre-vertibule fascia are related. So that's all about the facial layers of neck in brief. In subsequent lectures we shall discuss in detail the clinical significance of important facial spaces and how autotogenic infection spreads to each of them. Thank you.