Anatomy for the Royal College of Radiologists Fellowship. Malcolm Sperrin
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1 Third ventricle.
2 Left lateral sulcus (or lateral fissure/Sylvian fissure).
3 Right hippocampus.
4 Right superior temporal gyrus.
5 Septum pellucidum.
Comments:
The hippocampus is a grey matter structure most readily identifiable on coronal images. It lies on the medial side of the temporal lobe, immediately inferior to the temporal horn of the lateral ventricle. The amygdala is anterior to the hippocampus, and curls round to lie anterior and superior to the temporal horn of the lateral ventricle.
The fornix is a C-shaped white matter tract that arises posteriorly from the hippocampus. One crux of the fornix arises from each hippocampus, and curls superiorly and anteriorly until it joins with the contralateral crux. These form the body of the fornix which lies immediately below the septum pellucidum. As it continues anteriorly, the fornix splits again into two columns. Each column travels in an inferoposterior arc behind the anterior commissure and then lateral to the third ventricle. It then meets the ipsilateral mamillary body. The mamillary bodies lie at the base of the brain below the third ventricle and are seen anterior to the midbrain on MRI.
Exam tip:
The distinction between the hippocampus and the amygdala is difficult on a single coronal image. However, the amygdala is located more anteriorly, and we would not expect to see it together with the brainstem on the same coronal image.
Q1.10 Coronal image from a CT angiography study with intravenous contrast
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 Superior sagittal sinus.
2 Straight sinus.
3 Left sigmoid sinus.
4 Tentorium cerebelli.
5 Falx cerebri.
Comments:
The falx cerebri is a fold of dura mater which is situated in the interhemispheric fissure and divides the two cerebral hemispheres. It attaches to the crista galli anteriorly and to the tentorium cerebelli posteriorly.
The tentorium cerebelli is another fold of the dura mater, which lies above the cerebellar hemispheres. The falx cerebri splays slightly where it meets the tentorium, creating a pouch which contains the straight sinus.
Exam tip:
Remember to read the description at the start of the question as it can give useful clues to identify structures. In this case, the information about contrast administration gives a clue that hyperattenuating structures may be vascular—namely, cerebral venous sinuses. However, bear in mind that other structures might still appear bright even though they aren’t vascular—as with the falx cerebri and tentorium in this image.
Q1.11 T1-weighted sagittal section from an MRI of the 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 Dorsum sellae.
2 Cerebellar tonsil.
3 Basion.
4 Clivus.
5 Pituitary infundibulum.
Comments:
The sella turcica (also known as the hypophyseal or pituitary fossa) is a hollow in the sphenoid bone which contains the pituitary gland. The anterior boundary of the pituitary fossa is the tuberculum sellae, above which are two small processes called the anterior clinoid processes. The posterior boundary of the pituitary fossa is the dorsum sellae (‘back of the seat’), which is continuous inferiorly with the clivus. Two processes at top of the dorsum sellae are known as the posterior clinoid processes.
The clivus is a backward-sloping structure in the skull base which is formed by part of the sphenoid bone superiorly and part of the occipital bone inferiorly. Posterior to the clivus sits the basilar artery and the pons. The inferior tip of the clivus is an anatomical landmark known as the basion—this is the anterior margin of the foramen magnum.
Exam tip:
On a T1-weighted MRI, the posterior part of the pituitary gland (neurohypothysis) is brighter than the anterior pituitary (adenohypothysis).
Q1.12 3D reconstruction of a phase contrast angiography MRI sequence
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 Superior anastomotic vein (Vein of Trolard).
2 Vein of Galen.
3 Inferior anastomotic vein (Vein of Labbé).
4 Basal vein (of Rosenthal).
5 Superior sagittal sinus.
Comments:
The superior anastomotic veins (Veins of Tolard) connect the superior sagittal sinus to the superficial middle cerebral veins, which ultimately drain to the cavernous sinuses. The inferior anastomotic veins (Veins of Labbé) connect the transverse sinuses to the superficial middle cerebral veins.
The right and left basal veins of Rosenthal join with the internal cerebral veins to form the vein of Galen, which is short and runs within the quadrigeminal cistern. This then combines with the inferior sagittal sinus to form the straight sinus, which drains into the confluence of the sinuses.
Exam tip:
This is a difficult question. The superior and inferior anastomotic veins can be identified because they are large veins draining into the superior sagittal sinus and transverse sinus,