DR 1 - Skull and Cranial Cavity DEMO COPY(1).pdf

Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. 202 DR1: Skull and Cranial Cavity Learning Outcomes: By the end of the module you should be able to: • Identify the layers of the scalp • Identify of the bones of the skull • Describe the blood supply to the brain • Identify...

Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. 202 DR1: Skull and Cranial Cavity Learning Outcomes: By the end of the module you should be able to: • Identify the layers of the scalp • Identify of the bones of the skull • Describe the blood supply to the brain • Identify the features of the base of the skull • Name the cranial foramina and the structures which pass through them • Appreciate the anatomy as depicted in clinical imaging and identify pathological signs Welcome back to the Anatomy Laboratory. In this module we will focus on elements of head and neck anatomy with a particular focus on the relations of the brain and cranial nerves. The head and neck are demanding but interesting regions in which you will find many important structures crowded into a relatively small space. In addition to the brain and the special sense organs, this region also houses the upper parts of the digestive and respiratory tracts. 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. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 1 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Workstation 1. Scalp, skull and embryology In this workstation you will examine the bony skull and its development. A. Examination of the scalp and skull 1. Using the prosection identify the five layers of the scalp – Skin Connective tissue Aponeurosis Loose areolar connective tissue Periosteum The skull is comprised of the neurocranium (cranium) and the viscerocranium (or facial skeleton) and is comprised of 22 bones. The neurocranium contains 8 bones (occipital, two temporal, two parietal, sphenoid, ethmoid and frontal). The viscerocranium 14 bones (two nasal conchae, two nasal bones, two maxilla, two palatine bones, two zygomatic bones, two lacrimal bones, vomer, mandible). 2. Using the images below and the iPads, identify the bones of the skull. Lateral view of the skull Internal surface of lateral aspect of the skull. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 2 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Anterior aspect of the skull B. Embryology - development The two main parts of the skull are the calvarium (or brain case) and the facial skeleton. The post-natal growth of the two components proceeds at different rates. At birth, although the skull is large in proportion to the rest of the skeleton, the facial skeleton is relatively small with the exception of the large orbits. The calvarium is relatively large at birth and accommodates the large and rapidly growing brain. The growth of the calvarium proceeds rapidly (in pace with the developing brain) enlarging in a concentric fashion during the first year. Between the first and seventh year, the growth rate is reduced. After about the seventh year, growth is even slower and adult dimensions are normally reached by the 15th or 16th year. Ossification of the skull bones is incomplete at birth and many of the "bony" elements are united by fibrous tissue, either linearly or at large areas called fontanelles which are the so called "soft spots". Examine the neonatal skulls and locate the different bones and sutures. 1. Locate the large anterior fontanelle that closes by the end of the second year. 2. Locate the posterior and anterolateral (sphenoid) fontanelles that close after 2-3 months 3. Locate the mastoid fontanelles that close by the end of the first year. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 3 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. The development of the facial skeleton largely depends on the growth of the mandible and on the enlargement of the nasal cavities and paranasal air sinuses. These cavities may not achieve full development until late childhood. Maxillae – are carried downwards and forwards by the enlargement of the sinuses thus contributing substantially to the shape of the face. The maxillae accommodate the developing teeth until at least 6 months of age when the deciduous teeth start to erupt. At birth, the mandible is in two halves united at the symphysis menti in the median plane. Ossification occurs here at about the end of the first year. After the appearance of the permanent teeth (6 years onwards), the mandible increases in depth and elongates to accommodate the erupting teeth, and to ensure correct alignment with the teeth of the maxillae. Thus, the angle between the ramus and body of the mandible becomes a right angle. The temporal bone develops in four pieces corresponding to the four parts of the adult. At birth, the internal ear, tympanic cavity, auditory ossicles and mastoid antrum are almost fully developed however the tympanic plate is an incomplete ring and the mastoid process has still to develop. The external auditory meatus is poorly developed and the ear drum lies close to the surface where it is prone to injury. Owing to the absence of the mastoid process in the neonate, the stylomastoid foramen, and therefore the facial nerve, are exposed on the lateral surface of the skull and are liable to injury. As the infant begins to turn its head, the mastoid process enlarges. The mastoid process is invaded by air sacs from about the 6th year of age. The tympanic plate enlarges to form the bony part of the external auditory meatus. The growth of the base of the skull is responsible for much of the lengthening of the skull. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 4 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. The image to the left depicts fetal skull from the superior and lateral aspect. 4. Examine the historical embryology pots, identify the developing skull bones and the fontanelles. Examine the different stages of development of the vertebral column. 5. Examine the x-ray of the child skull locate the; mandible, deciduous teeth and the developing permanent teeth. What is the name given to extra bones that can be created in the skull in-between sutures? Wormian bones / intrasutural bones / sutural bones Skull and Cranial Cavity Dominic O’Brien 9/30/2022 5 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Clinical Context Scalp wounds and infections The ‘L’ in SCALP or Loose connective tissue is known as a danger area clinically because blood or pus can spread easily along it. Through what structures will the infection be able to pass through to reach the cranial cavity? Blood vessels What condition can be caused if the infection reaches the meninges? Meningitis Infections in the scalp cannot pass easily into the neck due to the attachment of the occiptofrontalis muscle on the posterior aspect, however it is possible for infection or blood to pass to the face on the anterior aspect. This is termed Ecchymosis. Lacerations to the scalp can bleed for a prolonged period if the wound is not closed correctly. Which layer of the scalp, in addition to the skin, needs to be sutured to ensure proper would closure? Aponeurotic layer Skull and Cranial Cavity Dominic O’Brien 9/30/2022 6 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Workstation 2. Blood Supply A. Blood Supply The blood supply to the head and neck arises from carotid and vertebral arteries. The common carotid artery in the neck divides into the internal and external carotid arteries. The internal carotid artery continues straight into the skull without branching, entering the skull via the carotid canal. The external carotid gives of several branches in the neck, face and head before terminating in the superficial temporal artery. More details of this artery are covered in later sessions. The vertebral arteries arise from the subclavian artery and passes through the transverse foramina in cervical vertebrae before entering the skull through foramen magnum. The vertebral arteries unite in the vicinity of the pons to form the single basilar artery. The basilar artery subsequently divides at the level of the superior border of the pons into the posterior cerebral arteries, which supply the inferior surface and occipital pole. The main arterial vessels form an anastomosis at the base of the brain, which is known as the cerebral arterial circle. The circle is formed by the posterior cerebral, posterior communicating, internal carotid, anterior cerebral and anterior communicating arteries. Examine the plastic brains showing the cerebral arterial circle (circle of Willis). 1. Identify the following arteries: Vertebral, Basilar, Inferior and Superior cerebellar, Posterior, Middle and Anterior cerebral. anterior cerebral artery middle cerebral artery posterior cerebral artery vertebral artery Skull and Cranial Cavity Dominic O’Brien anterior communicating artery internal carotid artery posterior communicating artery basilar artery 9/30/2022 7 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. What might be the signs and symptoms of a TIA? Remind them of the FAST campaign Face – drooping Arms – Loss of control Speech - slurred, incoherent Time – being important for treatment The main veins draining blood from the brain are the cerebral veins of which there are a number based on their location and territory of drainage. 2. You should try and identify the anterior and middle cerebral veins, which drain into the basal veins before reaching the great cerebral vein. Other veins such as inferior cerebral veins may also be visible. Venous drainage from the brain enters the dural venous sinuses, which eventually drain into the internal jugular vein at the jugular foramen in the base of the skull. anterior cerebral vein middle cerebral vein basal vein great cerebral vein The image above depicts the veins draining the brain. What is the result of a sudden occlusion in one of the main arteries of the brain? Cerebral infarction Lack of blood supply – and thus oxygen and nutrients to the brain – which can cause portions of the brain to die. Depending on which portion of the brain this occurs within, will depend on what signs and symptoms are seen. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 8 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Clinical Context Stroke A stroke is an acute disruption of normal blood supply to the brain that results in the death of brain cells, resulting in brain malfunctions. 1. Take turns to examine the pot ED14 or use the link to see the pot showing an aneurysm. 2. A stroke is caused by a disturbance in the blood supply to the brain, either due to a blockage of a blood vessel by arterial embolism, or by hemorrhage. Using the arteriogram identify the cerebral arteries. Can you see any abnormalities? The image above depicts an arteriogram of the cerebral arteries. 3. Take turns to examine pot ED9 or use the QR code to view the pot which shows a complete loss of the cortex, which vessel was occluded? Skull and Cranial Cavity Dominic O’Brien 9/30/2022 9 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Workstation 3. Cranial Base A. Cranial Nerves Cranial nerves are unique because they emerge from the brain and hence cranial cavity to carry sensory and/or motor fibres to innervates muscles or glands and carry impulses from sensory receptor. The twelves pairs are ordered in a rostral to caudal orientation. To leave the cranial cavity they pass through foramina. Can you recall the twelve cranial nerves? 1. Using the iPads, identify each of the foramina and which cranial nerve(s) and or artery passes through them. Use the provided pipe cleaners labelled with each structure, and place through the correct foramen of the skull models. (PLEASE DO NOT USE THE HUMAN MATERIAL FOR THIS ACTIVITY) The image above depicts the foramen of the anterior, middle and posterior cranial fossa. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 10 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. This image depicts the cranial nerves as they emerge from the brain (this will be covered in the next DR session). Note how these align with the foramina through which they exit. You will cover each of the cranial nerves in further detail over the next sessions. Why might it be important to have knowledge of the cranial foramina and the structures which pass through them? Head/skull injuries – if you know what are is damaged and what structures are close by, you may be able to anticipate/make sense of the signs and symptoms seen. What structures are at risk of injury in an individual who suffers a fracture in their posterior cranial fossa? Spinal cord Brainstem Cranial nerve which arise from the lower levels of the brainstem (CN VI, VII etc.) Vertebral arteries Basilar artery etc. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 11 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Clinical Context Cranial base injury The image above displays a fracture in the cranial base, specifically in the sphenoid bone. Which endocrine structure is at risk of damage in the injury depicted above? Pituitary gland This injury can result in persistent rhinorrhoea (runny nose). Why might this happen, and what fluid is exiting the nasal cavity? Damage to the meninges causing a CSF fistula. CSF then leaks into the nasal cavity. Cranial base injuries and pathologies of the CNS may require surgical intervention. What surgical approaches would likely be taken to access these areas? Endoscopic / minimally invasive surgery Entry through pre-exiting openings – orbit, nasal and oral cavity Possibility of open surgery in more extreme cases. Skull and Cranial Cavity Dominic O’Brien 9/30/2022 12 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Workstation 4: Imaging Pathologies of the Skull and Cranial Cavity Extradural and subdural haematomas Case 1 - Radiopaedia Patient age: 10 years old Presentation: Head injury from rotating fan blades Axial non-contrast CT Gender: Male Sagittal non-contrast CaseCT 2 – Radiopaedia Patient age: 65 years old Gender: Male Presentation: Confusion and shortness of breath in patient with history of alcohol abuse. Axial non-contrast CT Coronal non-contrast CT Discuss the cases presented on the previous page, thinking about the following: - Signs and symptoms the patient would present with - Which case is an example of an: o Extradural haematoma? Case 1 o Subdural haematoma? Case 2 o How is it possible to tell the difference on the CT scans? Concave vs. convex Skull and Cranial Cavity Dominic O’Brien 9/30/2022 13 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Metastatic Cancer Case 3 - Radiopaedia Patient age: 45 years old Gender: Female Presentation: Known for breast cancer, presented with a history of progressive painless swelling of the region. Discuss the cases presented above, thinking about the following: - Through what systems could this cancer have spread? o Lymph, blood - Which part of the skull is this metastasis located in? o Parietal bone - Is there any involvement of brain tissue in the metastasis? o Nope - What medical interventions could be taken to treat this case? o Surgical excision, radio/chemotherapy Skull and Cranial Cavity Dominic O’Brien 9/30/2022 14 Module 202: Neuroscience and Behaviours: Skull and Cranial Cavity. Checklist Review all the structures you have examined today and ensure that your demonstrator is satisfied that you have completed the check list below before you leave the dissecting room: • Identify the layers of the scalp • Identify of the bones of the skull • Describe the blood supply to the brain • Identify the features of the base of the skull • Name the cranial foramina and the structures which pass through them • Appreciate the anatomy as depicted in clinical imaging and identify pathological signs Skull and Cranial Cavity Dominic O’Brien 9/30/2022 15