Anatomy for the Royal College of Radiologists Fellowship. Malcolm Sperrin

structure.

      5 Name the arrowed structure.

       Answers

      1 Left middle cerebellar peduncle.

      2 Cerebellar vermis.

      3 Right temporal lobe.

      4 Right trigeminal nerve.

      5 Right optic nerve.

       Comments:

      The main cranial nerves that are identifiable on cross-sectional imaging and are therefore most likely to appear in the exam are the optic nerve, the trigeminal nerve, the facial nerve and the vestibulocochlear nerve. The trigeminal nerve, which provides sensory input from the face and also innervates the muscles of mastication, arises from the anterior pons. It travels anteriorly through the prepontine cistern and into the trigeminal (Meckel’s) cave, where it forms the trigeminal (Gasserian) ganglion. At this point, it divides into three branches. V1 (the ophthalmic nerve) passes through the cavernous sinus and then the superior orbital fissure. V2 (the maxillary nerve) also passes through the cavernous sinus, and exits the skull through the foramen rotundum. V3 (the mandibular nerve) exits the skull through the foramen ovale.

      The optic nerve arises at the retina, and travels posteriorly through the orbit to enter the skull through the optic canal. It then passes through the suprasellar cistern to join with the contralateral optic nerve at the optic chiasm. Nerve fibres then travel in two optic tracts to the lateral geniculate nuclei.

      The cerebellar peduncles are three paired white matter tracts that connect the brainstem with the cerebellum. The middle cerebellar peduncles are the largest of these, and connect the pons and cerebellum. The superior and inferior cerebellar peduncles connect the cerebellum with the midbrain and medulla, respectively.

       Exam tip:

       The trigeminal (Meckel’s) cave isn’t shown on this image, but is a classic exam question—make sure you’re familiar with identifying it on an axial MRI section.

Q1.7 Midline sagittal image from a T2-weighted MRI brain

      1 Name the arrowed structure.

      2 Name the arrowed structure.

      3 Name the arrowed structure.

      4 Name the arrowed structure.

      5 Name the arrowed structure.

       Answers

      1 Splenium of the corpus callosum.

      2 Tectal (quadrigeminal) plate.

      3 Pituitary gland.

      4 Mamillary body.

      5 Genu of the corpus callosum.

       Comments:

      The midline sagittal section commonly appears in examinations because it demonstrates a lot of anatomy. It is important to recognise the brainstem structures of the midbrain, pons and medulla, and also the cerebral aqueduct and fourth ventricle.

      The midbrain is divided by the plane of the cerebral aqueduct into the larger tegmentum ventrally and the smaller tectum dorsally. The tectum is often referred to as the tectal (quadrigeminal) plate, and is readily identifiable on sagittal images.

      The corpus callosum links the right and left cerebral hemispheres and is divided into four main parts from anterior to posterior: the rostrum, the genu (knee), the body, and finally the more bulbous splenium (meaning bandage). Additionally, the thin section between the body and splenium is sometimes described as the isthmus.

      The thalami sit on either side of the third ventricle. They are connected by a band of tissue called the massa intermedia (interthalamic adhesion), although this is not present in all patients.

       Exam tip:

       Note that some of the structures in the upper spine are demonstrated here—including the dens and the anterior and posterior arches of C1.

Q1.8 Axial image from T2-weighted sequence of MRI brain

      1 Name the arrowed structure.

      2 Name the arrowed structure.

      3 Name the arrowed structure.

      4 Name the arrowed structure.

      5 Name the arrowed structure.

       Answers

      1 Left external capsule.

      2 Posterior limb of the left internal capsule.

      3 Right extreme capsule.

      4 Right claustrum.

      5 Head of the left caudate nucleus.

       Comments:

      The basal ganglia are deep (i.e. not at the cortical surface) grey matter structures. The paired caudate nuclei are tucked in beside the lateral ventricles—they are comma-shaped, with the bulbous head of the caudate nucleus anteriorly. The other main structure in the basal ganglia is the lentiform nucleus comprising the putamen and the globus pallidus (these are not distinguishable on the image in this question). This is separated from the caudate nucleus by the internal capsule. The internal capsule is a white matter structure which is a major avenue of communication between the cortex and the lower CNS; for example, the corticospinal tract passes through it. It is divided into three parts—the anterior limb (between the lentiform nucleus and caudate nucleus) and the posterior limb (between the lentiform nucleus and thalamus), which are connected by the genu (‘knee’).

      Beyond the lentiform nucleus is an onion-skin of structures—the external capsule (a white matter tract) beyond which is the claustrum (a strip of grey matter). Next along is another white matter tract, the extreme capsule, followed by the insular cortex.

       Exam tips:

       The axial view through the basal ganglia is another exam classic. Also make sure to be familiar with the anatomy in coronal views.

       Cavum septum pellucidum and cavum vergae are often shown on coronal sections—look out for these if the question asks for an anatomical variant.

Q1.9 T1-weighted coronal slice from an MRI in an adult patient

      1 Name the arrowed structure.

      2 Name the arrowed structure.

      3 Name the arrowed structure.

      4 Name the arrowed structure.

      5 Name the arrowed structure.