2 17 Anatomy of IOM Posterior fontanel Sagittal suture Coronal sutures Anterior fontanel Fig. 2.8 Superior view of the infant skull showing the anterior and posterior fontanelles along with the development of the sagittal and coronal sutures into this space as a result of trauma or the spontaneous rupture of a blood vessel can enlarge this space causing compression on the brain. This is known as a subarachnoid hemorrhage and requires surgical intervention to decompress the neural tissue. The dura and arachnoid are normally attached closely. Occasionally bleeding resulting from trauma or disease will occur opening up a space between the dura and arachnoid that does not normally exist. This potential space is called the subdural space, and the resulting bleed or clot would be known as a subdural hemorrhage or subdural hematoma, respectively. The Ventricles mater, and the pia mater. The term dura mater is from the Latin literally meaning âtough mother,â while pia mater means âsoft mother.â The word arachnoid implies a spider weblike quality. The function of the meninges is to protect the brain and contain cerebrospinal fluid (Fig. 2.9). The dura mater is the fibrous outermost layer of the meningeal membranes. This layer contains larger blood vessels as well as sensory nerve fibers. Among the blood vessels present in the dura mater are large venous sinuses that return blood and cerebrospinal fluid from the brain back to the heart. There are two dural extensions that you should be familiar with. The falx cerebri separates the cerebral hemispheres and the tentorium cerebelli separates the occipital lobe from the cerebellum (Fig. 2.10). The arachnoid mater is thinner than the dura and resembles a loose fitting sac for the brain. Thin filaments known as arachnoid trabeculae extend from the arachnoid to the pia mater. The pia mater is the thinnest layer of the meninges and closely adheres to the surface of the brain and spinal cord following each gyrus and sulcus. The pia has an extensive capillary network that nourishes the surface of the brain and spinal cord. There is a normally occurring space between the arachnoid and pia mater. This subarachnoid space is filled with cerebrospinal fluid. Bleeding There are a series of canals within the brain whose function is to circulate cerebrospinal fluid. These are known as the cerebral ventricles (Fig. 2.11). There are two paired (left and right) lateral ventricles, a third ventricle, and a fourth ventricle. The ventricles communicate with each other via foraminal openings and are continuous with the central canal of the spinal cord. The left and right ventricles communicate with the third ventricle through the intraventricular foramina (of Monro). The third ventricle communicates with the fourth through the cerebral aqueduct (also known as the aqueduct of Sylvius). Cerebrospinal fluid returns to the subarachnoid space and venous circulation from the fourth ventricle via the midline foramen of Magendie and two paired foramina of Luschka. The cerebrospinal fluid (CSF) bathes and cushions the brain and spinal cord and is contained within the dura mater. The CSF is produced by tufts of tiny capillaries called choroid plexus that are found within the ventricles (Fig. 2.12). CSF is simply filtrated blood plasma. CSF comes from the blood and must eventually return to the blood. The presence of microorganisms or white blood cells in CSF indicates infection within the central nervous system. CSF can be sampled for diagnostic purposes by lumbar puncture.