DR 5 - Face, Temporal and Infratemporal Fossa PDF

Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. 202 DR5: Face, temporal and infratemporal fossa Learning Outcomes: By the end of the module you should be able to: • Identify the main muscles of the face • Describe the sensory and motor innervation to the face (cr...

Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. 202 DR5: Face, temporal and infratemporal fossa Learning Outcomes: By the end of the module you should be able to: • Identify the main muscles of the face • Describe the sensory and motor innervation to the face (cranial nerve 5 and 7) • Identify the parotid gland and the facial nerve and its branches • Identify the arterial supply and venous drainage of the face • Locate the muscles of mastication and their nerve supply (cranial nerve 5) • Identify the major contents of the temporal and infratemporal fossa • Apply clinical examples to anatomical principles In this practical session you will study the anatomy of the face. You will explore the temporal fossa and the muscles of mastication and the contents of the infratemporal fossa, including relations with the trigeminal nerve. For this session you will examining a range of prosected specimens as well as the anatomical models available within the dissecting room. As with all your other practical sessions in the dissecting room make sure you work through this handout, answer the questions and complete the checklist. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 1 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Workstation 1. Face In this workstation you will examine the muscles of facial expression, the parotid gland and facial nerve. A. On the face examine the facial muscles and parotid gland. 1. Locate as many muscles of facial expression as you can, using the figure below to help you. You will only be examined on the muscles mentioned here and in the lecture: - Occipitofrontalis - Orbicularis oculi - Orbicularis oris - Zygomaticus - Platysma These are innervated by the facial nerve. Consider the actions each muscle creates. 2. Identify the extent of the parotid gland. 3. Locate the parotid duct. 4. Locate the opening of the parotid duct in the oral cavity, which pierces through buccinators. You may be able to find this on the prosection, or yourself by moving your own tongue over the lining of your check opposite your second upper molar. 5. Identify the facial nerve over and within the parotid gland. To test the muscles, you would ask a patient to crease up their forehead (raise their eyebrows), close their eyes and keep them closed against resistance, puff out their cheeks and reveal their teeth. 6. Using the mirrors or ask a colleague to undertake these movements, and identify which muscles are responsible for each action. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 2 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. The image above depicts the muscles of facial expression. What is the function of the parotid gland? Secretion of saliva into the oral cavity to begin the digestive process. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 3 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. B. The facial nerve (CN7). 1. Using the skull trace out the route that the facial nerve makes. The following paragraph may be helpful. The facial nerve has two roots, a large motor root and a smaller nervus intermedius that consists of both sensory and parasympathetic fibres. Both roots arise at the cerebellopontine angle and pass with the vestibulocochlear (CN 8) nerve and the labyrinthine artery into the internal acoustic meatus. Both roots of the nerve traverse the petrous temporal bone in the facial canal (not possible to see). Within the temporal bone several small branches arise from the facial nerve. Some of these pass anteriorly to supply the pterygopalatine ganglion; postganglionic fibres are distributed to the lacrimal gland (through the lacrimal branch of the ophthalmic nerve) and to the glands and mucous membranes of the nasal cavity and palate. The sensory root is finally distributed as the chorda tympani nerve which supplies taste to the anterior 2/3rds of the tongue and conveys parasympathetic fibres to the submandibular ganglion (see DR Session 5). The motor root of the facial nerve gives a branch to the stapedius muscle before passing out of the skull via the stylomastoid foramen. 2. Locate the motor roots on the prosection. The motor root sweeps laterally and forward, giving branches to the posterior belly of digastric and to the stylohyoid muscle before entering the parotid gland. Within the parotid gland the nerve divides into five terminal branches to supply the muscles of the face and scalp. From superior to inferior the branches are: - Temporal - Zygomatic - Buccal - Mandibular - Cervical Another branch posterior auricular passes posteriorly behind the ear. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 4 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. The image above depicts branches of the facial nerve. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 5 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. C. Examine the blood supply and venous drainage of the face. The face is richly supplied with superficial arteries and veins. The arteries are derived from the external carotid artery. 1. Identify the external carotid artery 2. Trace the artery superiorly until it terminates in the superficial temporal artery 3. Moving inferiorly, locate the other terminal branch the maxillary artery 4. Moving inferiorly again locate the facial artery as it winds its way to the angle of the mouth and then superiorly up to the nose and medial of the orbit. Most veins accompany the arteries and there is great variation and anastomoses. The retromandibular vein is a deep vein of the face that is formed by the union of the superficial temporal vein and the maxillary vein, latter with venous blood joining from the pterygoid plexus. The retromandibular vein drains into the external jugular vein and eventually subclavian vein. 5. Locate the facial vein, superficial temporal vein & retromandibular vein This image depicts the arterial supply and venous drainage of the face. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 6 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Clinical Context Facial Nerve Palsy (Bell Palsy) Injury to the facial nerve or its branches can produce paralysis of some or all of the facial muscles on the affected side, thus changing facial expression. The palsy also affects the tone of muscles which in turn can cause the inferior eyelid to evert. This creates problems as lacrimal fluid is not held within the eye and can mean that the corneal surface doesn’t have enough lubrication; so becomes dry and can scar. The palsy can also affect the buccinator and orbicularis oris muscles. These muscle assist in keeping the food bolus in the mouth, so if they become paralysed the patient can find that food becomes lodged in the oral cavity and needs to be removed with a finger. It can also result in the mouth becoming displaced at the edge meaning that saliva can dribble out. The palsy can also affect the way the mouth moves to create speech meaning the patient has a limited ability to make sounds. Differentiating between Facial nerve injury and stroke During clinical examination, (amongst other tests), a patient with hemi-facial weakness will be asked to raise their eyebrows. In conditions such as Bell’s Palsy and Ramsay Hunt Syndrome, the forehead on the affected side will not be spared. However, in the presence of a stroke, the forehead on the affected side will be spared, and the creases will be the same. - Does the patient in the image to right present with a facial nerve injury or a stroke? Facial nerve injury due to lack of forehead creases on affected side. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 7 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Workstation 2. Muscles of mastication and maxillary artery. In this workstation you will examine the muscles of mastication and the blood supply to the infratemporal fossa. The temporal region is the lateral area of the scalp. The indentation (fossa) is occupied by the temporalis muscle. The infratemporal fossa is the space deep and inferior to the zygomatic arch, deep to the ramus of the mandible and posterior to the maxilla. A. On the face examine the muscles of mastication 1. Identify the temporalis muscle. Examine the different orientation of the fibres that account for its different actions. 2. Follow the temporalis muscle from its origin on the temporal bone to its insertion on the edge and medial surface of the coronoid process of the mandible and along the edge of the ramus of the mandible. Note that the insertion is very tendinous. 3. Identify the masseter muscle, like the temporalis is a muscle of mastication. Note the origin of the masseter on the zygomatic bone (superficial part) and zygomatic arch (deep part) and its multiple insertions onto the lateral surface of the ramus. This image depicts the temporalis and masseter muscles. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 8 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. 4. Identify the infratemporal fossa, which is a wedge-shaped cavity that lies inferior to the temporal fossa and between the ramus of the mandible and the wall of the pharynx. 5. Try to locate the contents of the infratemporal fossa, which are as follows: - the lower part of temporalis - the lateral and medial pterygoid muscles - the maxillary artery and its branches - the pterygoid venous plexus - the mandibular and chorda tympani nerves and the otic ganglion. 6. Locate the medial pterygoid. The medial pterygoid has two heads with the deep head originating from the medial surface of the lateral pterygoid plate of the sphenoid bone, and the superficial head arising from the maxilla. Both heads insert at the angle of the mandible and enable elevation and sideto-side movement of the mandible. 7. Locate the lateral pterygoid. The lateral pterygoid also has two heads. The upper head is not easy to see and arises on the roof of the fossa. The lower head is more visible, and you should find it originating from the lateral surface of the lateral pterygoid plate. Both heads insert into the neck of the mandible and the capsule of the temporomandibular joint. What makes the lateral pterygoid muscle different from the other muscles of mastication? Horizontal orientation of the muscle fibres This image depicts the medial and lateral pterygoid muscles. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 9 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. B. Maxillary artery The maxillary artery is the largest branch of the external carotid artery and can be found within the infratemporal fossa. The maxillary artery originates in the parotid gland and passes deep to the neck of the mandible and gives off several branches in the fossa. 8. Identify the maxillary artery. One of the most important branches of the maxillary artery clinically is the middle meningeal artery. This passes deep to the lateral pterygoid, between the roots of the auriculotemporal nerve to enter the skull via the foramen spinosum. In the specimens see if you can also identify the inferior alveolar artery, which runs inferiorly along with its nerve to the mandibular canal. 9. Identify the middle meningeal artery. This image depicts the middle meningeal artery and the inferior alveolar artery. Why is the middle meningeal artery of clinical importance? Vulnerable to injury during head trauma – lies beneath the suture point of several bones at the temples. The venous drainage of this area is through a dense pterygoid plexus around the pterygoid muscles. Veins corresponding to the branches of the maxillary artery open into this plexus which is drained by a maxillary vein. The pterygoid plexus communicates with the cavernous sinus and with the facial vein. The communications between intra and extra cranial veins can allow infections to spread into the cranial cavity. 10. Locate the pterygoid plexus. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 10 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Clinical Context Temporomandibular Joint Dysfunction (TMD) TMD covers a variety of symptoms involving pain and dysfunction of the TMJ and the muscles of mastication. There are multiple potential causes for these symptoms including arthritis, trauma, dislocation/subluxation, congenital abnormality and TMJ disk scarring or displacement. Management of the TMD depends on the underlying aetiology. Bruxism Bruxism is teeth grinding and can occur both when people are awake or asleep. There does not seem to be one cause, but rather many factors which play a part. Stress seems to be a factor, particularly in awake bruxism. Symptoms include headaches, tooth wear, hypertrophic masseters, pain during mastication and pain or clicking of the TMJ joint. This image compares healthy teeth and those displaying the effects of bruxism. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 11 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Workstation 3. Temporal/Infratemporal fossa and the trigeminal nerve. A. Mandibular branch of the trigeminal nerve. The mandibular (CN V3) nerve has a large sensory and a small motor root, supplying: - the skin in the temporal region, - part of the auricle (including the external auditory meatus and the tympanic membrane), - the lower lip and lower part of the face, - the lower teeth and gums, - the mucosa of the anterior two thirds of the tongue and the mucosa of the floor of the mouth. One of the sensory branches (auriculotemporal nerve) conveys postganglionic parasympathetic fibres from the otic ganglion to the parotid gland. The motor root of the mandibular nerve passes with the sensory root out of the posterior cranial fossa via the foramen ovale. The motor root supplies the muscles of mastication. 1. Identify the mandibular nerve. 2. Locate the foramen ovale and the otic ganglion As the mandibular nerve enters the infratemporal fossa through the foramen ovale, it is attached to the otic ganglion. The nerve supplies the medial and lateral pterygoids, tensor palatini, temporalis and masseter. It has a sensory branch the buccal nerve which supplies the cheek - not the buccinator muscle. 3. Examine some of the main branches of the mandibular nerve (CNV3) as it descends from the location of the foramen ovale (auricultemporal, lingual, inferior alveolar). Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 12 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. From the mandibular nerve the auriculotemporal branch passes around the middle meningeal artery to supply the external acoustic meatus, tympanic membrane and skin over the temple; it also carries parasympathetic fibres. The remainder of the posterior division of the mandibular nerve divides into the lingual and inferior alveolar nerves. The lingual nerve is joined by the chorda tympani (branch of facial nerve) as it crosses the medial pterygoid and passes into the floor of the mouth. The inferior alveolar nerve gives off a small motor branch to the mylohyoid muscle and continues as a sensory nerve. It enters the mandibular foramen on the medial aspect of the mandible and runs in the mandibular canal to supply the lower teeth. The terminal portion emerges at the mental foramen to supply the lower lip and chin. 4. Use the pot CX21 and/or the QR code with the iPads to trace out the branches of V1, V2 and V3. You will need to take this in turns. Why does the inferior alveolar nerve enter the mandibular foramen? To innervate the lower rows of teeth and gums. lingual nerve medial pterygoid inferior alveolar nerve nerve to mylohyoid The image above depicts the branches of the mandibular nerve. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 13 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Clinical Context Inferior Alveolar Nerve Blocks An inferior alveolar nerve block is frequently used in dentistry to anesthetize all mandibular teeth to the median plane. Because the nerve also supplies the skin and mucous membranes of the lower lip these areas are also affected and are noticed by patients. Problems can occur if during the injection anaesthetic is placed by accident into the parotid gland or the medial pterygoid muscle. Inferior Alveolar Nerve This image shows the path of the inferior alveolar nerve within the mandible. Where would the nerve block injection be administered within the oral cavity? Posteriorly within the oral cavity, as close as possible to the mandibular foramen - inferior to the TMJ. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 14 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Workstation 4: Imaging Pathologies of the Face, Temporal and Infratemporal Fossa Parotid gland neoplasms More than 90% of salivary gland tumours arise in the parotid gland and 75% of tumours are benign (Figure A). - Name the other glands which produce saliva. o Submandibular and sublingual salivary glands Their main risk factors are radiation exposure and genetic predisposition. Alcohol or tobacco use are not risk factors (as they form squamous tumours of the mouth), except for a benign tumour (Warthin’s tumour) which is associated with smoking history. The majority of benign tumours are pleomorphic adenoma (50%). The most common malignant tumour is mucoepidermoid carcinoma (15%) (Figure B). Metastasis of malignant tumours occurs to regional neck lymph nodes and the lungs. - What is the primary method of treatment for parotid gland neoplasms? Surgery - Which cranial nerve has a close relation to the parotid gland? CN VII / Facial nerve - How may a tumour in the gland affect this nerve, and what signs or symptoms would this produce? Impairment/paralysis of muscles of facial expression Figure A Figure B The images above depict tumours of the parotid gland. Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 15 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Infratemporal Fossa The MRI scans below show an individual with a well-defined mass in the right infratemporal fossa. Coronal T1 Weighted MRI - Axial T1 Weighted MRI What structures pass through the infratemporal fossa and could be affected by the tumour? o the lower part of temporalis o the lateral and medial pterygoid muscles, o the maxillary artery and its branches, o the pterygoid venous plexus, o the mandibular and chorda tympani nerves and the otic ganglion. - What potential effects would the compromise of these structures have? Impaired ability to chew due to impingement of muscles of mastication Impaired taste – chorda tympani Restricted blood supply to deep facial structures, dura mater (middle meningeal branch) Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 16 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. The Face The below scans come from a case of a 50-year-old male who had a previous injury of a shotgun blast to the face. 3D CT - Axial non-contrast CT From the 3D CT on the left, which bones of the facial skeleton were damaged in the injury? o Mandible and maxilla - What other important structures of facial anatomy may have been damaged during this injury? (i.e. neurovascular structures, musculature) o Muscles of the lower face, tongue, teeth, nasal cavity. - What is causing the streaking seen on the non-contrast CT on the right? o Lead pellets remaining in the patients face from the shotgun shell Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 17 Module 202: Neuroscience and Behaviours: Face, temporal and infratemporal fossa. Checklist Review all the structures you have examined today and ensure that you are satisfied that you have completed the check list below before you leave the dissecting room: • Identify the main muscles of the face • Describe the sensory and motor innervation to the face (cranial nerve 5 and 7) • Identify the parotid gland and the facial nerve and its branches • Identify the arterial supply and venous drainage of the face • Locate the muscles of mastication and their nerve supply (cranial nerve 5) • Identify the major contents of the temporal and infratemporal fossa Face, Temporal and Infratemporal Fossa Dominic O’Brien 9/30/2022 18