Anatomy and Positioning of the Skull, Abdomen, and Pelvis
Core concepts
Skull positioning relies on landmark lines: the orbitomeatal line, the interpupillary line, and the midsagittal plane. Know common projections such as PA, lateral, and Townes, and what each demonstrates. Abdominal positioning emphasizes supine and upright views, the role of the upright view for air-fluid levels, and the importance of collimation and shielding. Pelvis anatomy includes the iliac crests, symphysis pubis, and femoral heads; the AP pelvis requires the patient supine with the central ray at the level of the iliac crests or symphysis, depending on protocol.
Traps
Questions test which landmark aligns with which plane or line - for example, the orbitomeatal line perpendicular to the receptor for a lateral skull. A common trap is assuming an upright abdomen is always possible; if the patient cannot stand, a decubitus or supine view may be needed. Another trap is shielding the abdomen in a patient who may be pregnant - verify pregnancy status and follow protocol. Watch for confusion between AP and PA pelvis and what each shows.
Worked example / rule of thumb
For a suspected bowel obstruction, the upright abdomen demonstrates air-fluid levels that a supine view may not. Rule of thumb: align the landmark line to the receptor, then set the central ray; if positioning is limited, document and choose the alternative that best answers the clinical question.
Key points
- Skull positioning depends on landmark lines and planes.
- Upright abdomen shows air-fluid levels.
- Verify pregnancy status before abdominal exams.
- Pelvis centering depends on the structure of interest.
- Document limitations and choose the best alternative view.