Sample Lectures – How X-rays and CT Scans Work + Vignettes


 
 

Next Step: Make Cards on the Automatic Key Concepts, and Vignettes

Remember, the more you automatically know what each sentence means on your test, the better you will do. There are 4 stages in making interpretation more automatic:

  • Stage 1: Unable to Make Pathophysiologic Chronologies in Either Timed or Untimed setting
  • Stage 2: Basic Pathophysiologic Chronologies, but with Significant Gaps
  • Stage 3: Detailed Pathophysiologic Chronology Without Time, but Unable to Consistently Generate PC During Timed Setting
  • Stage 4: Consistent Pathophysiologic Chronologies in Timed Setting

My goal with these vignettes is to help you reach Stage 4. How do you do so?

  • With the Automatic Key Concept cards, you can master the underlying information to move past Stages 1 + 2.
  • Then, with the Vignette/Pathophysiologic Chronology cards, you can teach yourself to make these connections on your exam.

CT angiography: how is this different from a normal CT with IV contrast?

In both, you give IV contrast. However, in CT angiography, you time the CT so that most of the IV contrast is in the ARTERIES (before it reaches the capillaries), so you can better visualize the arteries

In our patient, this is what the CT angiography would have looked like

 

Intestinal pneumatosis – walk through the proposed pathophysiology to explain when this might be seen

Mesenteric ischemia (e.g. SMA occlusion) → bowel wall necrosis → breakdown of cell-cell adhesion / innate immune system → anaerobic bacteria translocation into bowel wall → infection of intestine wall → gas production as byproduct of anaerobic metabolism

 

 

Vignette/Pathophysiologic Chronologies:

Copy + paste these into your cards, to make the connections behind these vignettes more automatic.

An 82-year-old woman is brought to the emergency department 1 hour after developing sudden, severe pain in her right leg. She denies any recent trauma. On exam, her right lower extremity is cool and pale, with no pulses palpated. Minimal pain is elicited on palpation, however the patient otherwise appears extremely uncomfortable. EKG demonstrates an irregularly irregular rhythm.

What is the pathophysiologic chronology?

Summary:

Atrial fibrillation → L atrial clot → embolization to lower extremity artery → pulselessness / ischemia → severe, sudden pain

Detailed:

Atrial fibrillation → atrial blood stasis → L atrial clot forms → embolization to lower extremity artery → block of arterial flow → arterial pulsatility ↓ / ischemia → ischemic pain + pallor

 

A 64-year-old man presents with sudden, diffuse abdominal pain, and presents to the emergency department. He has a history of hypertension and an old myocardial infarction. He reports feeling nauseous, with diarrhea. Pulse is regular, and 110/min, with blood pressure 80/60 mmHg and respiratory rate 22/min. On abdominal palpation, minimal tenderness is elicited. EKG demonstrates sinus rhythm, with Q waves in leads V1-V4. CT with IV contrast demonstrates nonenhancement of the superior mesenteric artery with extensive intestinal pneumatosis.

What is the pathophysiologic chronology?

Summary:

Old LAD MI → LV hypokinesis → LV mural thrombus → embolization to SMA → acute mesenteric ischemia → intestinal pneumatosis

Detailed:

Old LAD MI → LV hypokinesis → LV mural thrombus → embolization to SMA → acute mesenteric ischemia

Pain out of proportion to exam: ischemia → minimal inflammatory cells / inflammation → minimal tenderness, despite severe pain

Intestinal pneumatosis: bowel wall necrosis → breakdown of cell-cell adhesion / innate immune system → anaerobic bacteria translocation into bowel wall → infection of intestine wall → gas production as byproduct of anaerobic metabolism

Non-enhancement of SMA: occlusion of SMA → electron-dense contrast won’t perfuse SMA → SMA non-enhancement via contrast

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