Anatomy, Embryology and Physiology Relevant to Imaging
Anatomy, embryology and physiology questions reward a three-dimensional model in your head. The exam tests whether you can place a lesion in the correct segment, explain a congenital anomaly from its embryological origin, and use physiological principles to predict imaging behaviour.
Embryology that is regularly examined
- Neural tube closure occurs around days 25-28; anterior failure gives anencephaly, posterior failure gives myelomeningocele.
- The midgut herniates, rotates 270° counterclockwise around the superior mesenteric artery and returns; incomplete rotation causes malrotation with SMA/SMV inversion and volvulus risk.
- Kidneys ascend from the pelvis; a horseshoe kidney is trapped below the inferior mesenteric artery at L3.
- First branchial arch gives mandible, malleus and incus; second gives stapes and styloid; third gives the hyoid body.
Anatomy rules worth memorizing
- Couinaud segments are defined by hepatic veins and portal pedicles; segment I is the caudate lobe.
- The right lung has 10 bronchopulmonary segments, the left 8-9; each has its own segmental bronchus.
- The circle of Willis is complete in only a minority; variants explain infarct patterns.
Worked example
A CT shows a 3-cm lesion in the right lobe above the right portal vein, between the middle and right hepatic veins. That is segment VIII (superior and anterior). Below the right portal vein it would be segment V. Naming the segment, not just the lobe, changes the surgical plan.
Traps
- Naming the lobe only when the segment is requested.
- Confusing right and left on axial images; the patient's right is on your left.
- Attributing an aberrant vessel to pathology when it is a normal variant.