66 ANATOMY FOR DIAGNOSTIC IMAGING
the cerebellar veins drain to the nearby dural sinuses as follows: • The superior and posterior parts to the straight and transverse sinuses; and • The inferior aspect to the inferior petrosal, sigmoid and occipital sinuses. Radiological features of the cerebellum CT and MRI On axial CT and MR sections taken through the pons (see Fig 2. 3a), the cerebellum is seen to be separated from the pons by the fourth ventricle and connected to the pons on each side of this by the middle cerebellar peduncles. At this level the cerebellum is bounded anteriorly by the petrous temporal bones. On higher slices (see Fig. 2. 3b) the cerebellum is separated from the temporal and occipital lobes anterolaterally the tentorial margins. Close to its bony attachment the tentorium can be easily seen on contrast-enhanced studies owing to the contained superior petrosal sinus. The superior vermis can be seen between the occipital lobes on sections through the thalamus. The normal flocculus enhances more than the rest of the cerebellum and should not be mistaken for a more anteriorly located acoustic neuroma. Fissures separating lobes of the cerebellum can be seen on sagittal MRI (see Fig. 2. 16). VENTRICLES, CISTERNS, CSF PRODUCTION AND FLOW VENTRICLES (Figs 2. 17-2. 19) These are fluid-filled spaces within the brain related to the development of the nervous system as a tubular structure with a central canal.
Fig. 2. 17 The ventricular system.
Two lateral ventricles represent expansion of the most anterior part of the ventricular system into each cerebral hemisphere. The third ventricle, the aqueduct and the fourth ventricle are midline in position and are continuous with the central canal of the cord. The ventricular system is also continuous with the subarachnoid space around the brain via foramina in the fourth ventricle. Approximately 25 mL of cerebrospinal fluid (CSF) fills these spaces in an adult. The ventricles are lined with ependyma, which is invaginated by plexuses of blood vessels called the choroid plexus. These vessels produce the cerebrospinal fluid. The lateral ventricles (see Fig. 2. 17) There is a lateral ventricle within each cerebral hemisphere. Each is C-shaped, with the limbs of the C facing anteriorly and a variably developed posterior extension from its midpoint. Each is described as having a frontal (anterior) horn, a body (atrium), a temporal (inferior) horn and an occipital (posterior) horn. An interventricular foramen (of Monro) at the junction of the anterior horn and the body connects each lateral ventricle with the third ventricle. Frontal (anterior) horn This extends into the frontal lobe. Its roof and anterior extremity are formed by the corpus callosum, its rostrum and genu, and fibres radiating from these, the tapetum. The head of the caudate nucleus makes a prominent impression in the floor and lateral wall of the anterior horn. The medial wall is formed by the septum pellucidum. There is no choroid plexus in the anterior horn. Body This is within the parietal lobe. As with the anterior horn, the roof and lateral wall of the body of the ventricle are
