AP Scout View
1. Posterior margin of foramen magnum is in proper position on this Towne's projection
2. Posterior clinoid
3. Dorsum sellae
4. Bracket encloses posterior fossa (primary area of interest)
5. Transverse sinus runs in the posterior edge of the tentorium cerebelli and this marks the separation between the posterior fossa and the posterior part of the supratentorial area
6. Anterior surface of the clivus. Projection should be nearly parallel to this surface.
Early Arterial Phase (1.5 sec post injection)
1. Left vertebral artery, cervical portion
2. Vertebral artery as it comes out of the C1 transverse foramen and rests on the top lateral portion of the C1 lamina
3. Muscular branches, vertebral artery
4. Contrast reflux into distal right vertebral artery.
5. Basilar artery
6. Posterior inferior cerebellar artery
7. Anterior inferior cerebellar artery
8. Superior cerebellar artery
9. Posterior cerebral artery
10. Calcarine branch of the posterior cerebellar artery. First portion projects lateral and the portion near the calcarine cortex is adjacent to the midline.
11. Parieto-occipital branch of posterior cerebral artery. First portion is medial, posterior portion is lateral.
12. Posterior inferior temporal branch, posterior cerebral artery
Early Arterial Phase (2 sec post injection)
1. Distal portion of the anterior inferior cerebellar artery loops either inside or adjacent to the internal auditory meatus. Displacement of this medially can be seen with acoustic neuromas.
2. Pontine artery, originates from basilar artery
3. Inferior vermian branch, posterior inferior cerebellar artery
4. Hemispheric branches, superior cerebellar artery
Late Arterial/Early Capillary Phase (5 sec post injection)
1. Note the area below the two transverse sinus grooves is lighter than the area above. This is because the contrast is in the capillaries of the cerebellum in the posterior fossa.
2. Note most of the contrast has been washed out of the vertebral and basilar arteries which are now being filled by unopacified blood.
3. The arteries which are seen above the transverse sinuses are branches of the posterior cerebral artery.
Mid-venous Phase (8 sec post injection)
1. Tonsillar veins
2. Vein of the lateral recess of the fourth ventricle
3. Petrosal vein
4. Superior petrosal sinus
5. Inferior vermian veins
6. Superior vermian vein
7. Region of precentral cerebellar vein
8. Straight sinus
9. Superficial cortical vein draining occipital lobe
10. Transverse sinus being filled from occipital lobe veins
11. Lower portion of transverse sinus being filled from the straight sinus