Lecture 1 - The Skull PDF

INTRODUCTION § The skull is the skeleton of the head. § A series of bones form its two parts: the cranium, and facial skeleton. § The cranium, or “cranial vault”, provides a case for the brain, brainstem, meninges, cranial nerves, and blood vessels. INTRODUCTION § The term cranium is restricted...

INTRODUCTION § The skull is the skeleton of the head. § A series of bones form its two parts: the cranium, and facial skeleton. § The cranium, or “cranial vault”, provides a case for the brain, brainstem, meninges, cranial nerves, and blood vessels. INTRODUCTION § The term cranium is restricted to the skull without the mandible. § The cranium has a dome-like roof called the calvaria, and a floor referred to as the cranial base consisting of the ethmoid and sphenoid bones, and parts of the temporal, occipital and frontal bones. INTRODUCTION The facial skeleton consists of the bones surrounding the mouth and nose and contributing to the orbits INTRODUCTION § The cranium in adults is formed by a series of eight (8) bones: § § § § § § A frontal bone Paired parietal bones Paired temporal bones An occipital bone A sphenoid bone An ethmoid bone INTRODUCTION § Most of these bones are flat, curved and joined by interlocking fibrous sutures. INTRODUCTION § The bones of the calvaria of a newborn are separated by areas of fibrous membranes - the fontanelles. § There are six (6) fontanelles: § Two (2) in the median plane § Anterior § Posterior § Two (pairs) on each side § Anterolateral or sphenoidal fontanelles § Posterolateral or mastoid fontanelles 18 to 24 months 6-8 weeks 3 months 1 or 2 months INTRODUCTION § The facial skeleton forms the anterior part of the skull containing the orbits and the nasal cavities and includes the maxilla and mandible. INTRODUCTION § The facial skeleton contains 14 irregular bones: § § § § § § § § Two (2) lacrimal bones Two (2) nasal bones Two (2) maxillae Two (2) zygomatic bones Two (2) palatine bones Two (2) inferior nasal conchae One (1) mandible One (1) vomer INTRODUCTION § In the anatomical position, the skull is oriented so that the inferior margin of the orbit and the superior margin of the external acoustic meatus (auditory canal) of both sides lie in the same horizontal plane (Frankfort horizontal plane) – auriculo-orbital plane. BONEY LANDMARKS OF THE SKULL Pterion = sphenoid, temporal, frontal, parietal Lambda = junction lambdoidal sutures Vertex = superior portion of the skull Bregma = forepart of the junction of the sagittal and coronal sutures Asterion = star-shaped, parietomastoid, occipitomastoid, lambdoid Glabella = prominence on frontal bone superior to root of nose Inion = most prominent point of external occipital protruberance Nasion = frontonasal and internasal junction BONY LANDMARKS OF THE SKULL § The pterion is the weakest part of the skull. § Located at the junction of the frontal, temporal, parietal, and sphenoid bones. § The group of sutures these bones form is H-shaped, resembling a “wing”. § The pterion is located in the temporal fossa, commonly known as the temple. § It is two finger breadths superior to the zygomatic arch, and a thumb breadth posterior to the zygomatic process of the frontal bone. § This is an important clinical landmark on the lateral aspect of the skull because the anterior branch of the middle meningeal artery (maxillary artery) lies in the groove on the internal aspect of the lateral wall of the skull. RADIOGRAPHIC APPEARANCE OF THE SKULL CLINICAL CORRELATIONS OF THE SKULL HEAD INJURIES § Head injuries are a major cause of disability. § The complications of head injury include vascular lesions such as hemorrhage, infection (e.g. osteomyelitis), and injury to the brain and cranial nerves. § Disturbance of consciousness is the most common complain. HEAD INJURIES § Head injuries are a scourge of industrialized society and current lifestyles. § They are a major cause of death, especially in young adults. § Few other conditions exceed the cost in human misery and dollars that head injuries cause. § Almost 10% of all death in the U.S. are caused by head injury, and approximately half of traumatic deaths involve the brain. HEAD INJURIES § Head injuries occur at all ages but mostly in young persons between the ages of 15 and 24. § Men are affected three or four times as often as women. § The major cause of brain injury varies but motor vehicle and motorcycle accidents are prominent. INJURY TO THE SUPERCILIARY ARCHES § The superciliary arches are relatively sharp ridges of bone. § Consequently, a blow to them (e.g. during a boxing match) may lacerate the skin and cause profuse bleeding. § Bruising of the skin surrounding the orbit causes tissue fluid and blood to accumulate in the surrounding connective tissue, which gravitates into the superior (upper) eyelid and around the eye - “black eye”. FRACTURES OF THE CALVARIA § The domelike shape of the skull distributes and minimizes the effects of a blow to it. § However, hard impacts to the head in thin areas of the cranium are likely to produce fractures. FRACTURES OF THE CALVARIA § TYPES OF FRACTURES: § Depressed fractures § A fragment of bone is depressed inward to compress or injure the brain. § Linear skull fractures § The most frequent type § Usually occurring at the point of impact § Fracture lines often radiate away from it two or more directions § Comminuted fractures § The bone is broken in several fragments COMMINUTED DEPRESSED FRACTURE OF THE LEFT PARIETAL BONE WITH UNDERLYING HEMORRHAGIC CONTUSION AND AIR EPIDURAL HEMORRHAGE Dura Mater adherent to sutures OK here * Shape Epidural Hemorrhage Time Delay Rupture of Bridging Veins Cerebral Veins Subdural Hematoma Subdural Hemorrhage SUBDURAL HEMORRHAGE SUBARACHNOID HEMORRHAGE Usually resulting from hypertension or ruptured aneurysm FRACTURES OF THE CALVARIA § If the area of the skull is thick at the site of impact, the bone usually bends inward without fracturing. § However, a fracture may occur some distance from the site of direct trauma where the calvaria is thinner. FRACTURES OF THE CALVARIA § In a contrecoup (counterblow) fracture, no fracture occurs at the site of impact but one occurs on the opposite site of the skull.