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Radiology Clerkship > Basics of CT interpretation > Flashcards

Basics of CT interpretation Flashcards

1
Q

Chest CT window interpretation

A
  1. Thyroid gland
  2. Lymph nodes (supraclavicular, subaxillary)
  3. Internal mammary artery and vein (lymph nodes here >4 mm are abnormal)
  4. Anterior diaphragmatic lymph nodes
  5. Paraesophageal/Paraaortic region
  6. Hilar region (R hilum usually has a ~9mm lymph node, which is normal)
  7. Esophagus/trachea up to thoracic inlet
  8. Thymic tissue (should have bits of fat inside)
  9. Heart, great vessels, and pericardium
  10. Pleura and diaphragmatic surface
  11. Put on lung window (MIP if available) and look at airways and lung parenchyma
  12. Bone window
  13. Muscle and subcutaneous fat
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2
Q

Abdominal CT window interpretation

A
  1. Liver (in smaller window – lesions often similar to normal tissue)
  2. Biliary tree (to ampulla)
  3. Pancreas
  4. Spleen
  5. Adrenals
  6. Kidneys
  7. Ureters to bladder
  8. GI tract starting at rectum and going to cecum, appendix, and terminal ileum
  9. GI tract starting at the esophagus and going to the proximal jejunum
  10. Mesentery and remaining small bowel
  11. Greater omentum
  12. Lesser omentum
  13. Vasculature (portal, arterial, venous)
  14. Lymph nodes
  15. Reproductive organs
  16. Muscular and subcutaneous tissues
  17. Bone window
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3
Q

Past what size do we call a lymph node “enlarged”?

A

Short axis of 10 mm

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4
Q

Cutoff for abnormally enlarged aorta and pulmonary artery

A
  • Aorta: 40 mm
  • Pulmonary artery: 30 mm
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5
Q

Mixing artifact

A
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6
Q

Rim enhancing mass on CT

A

Concerning for malingnancy/abnormality

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7
Q

When do you NOT use contrast?

A

When you are looking for things that area already bright on their own:

Bones

Extravasated blood

Stones

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8
Q

Types of oral contrast

A
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9
Q

Barium peritonitis

A

Peritonitis caused by barium contrast irritation of the peritoneum

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10
Q

When do we use volumen?

A

When we want to see natural enhancement from inflammation, especially in the bowel (IBD)

Note: You can also use water if you act quickly!

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11
Q

Indications for oral contrast

A
  • Thin patient
  • Prior bowel altering surgery
  • Inflammatory bowel disease (but for this we use Volumen!)
    • Note: SBO and ileus are NOT on this list
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12
Q

Indications for rectal contrast

A
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13
Q

Indications for contrast cystogram

A
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14
Q

Contrast reactions have greatly reduced since . . .

A

. . . we stopped using high osmolar contrast

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15
Q

Allergic-like contrast reaction

A

Epinephrine!!! (if airway is at risk)

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16
Q

Can a patient with a “contrast allergy” get contrast again?

A

You can premedicate with steroids and benedryl to reduce risk.

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17
Q

Contrast extravasation

A

Effectively contrast-induced compartment syndrome

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18
Q

Contrast induced nephropathy

A
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19
Q

Preventing CIN

A
  • Use iso-osmolar contrast
  • Preload with fluids
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20
Q

Two groups where you need to think twice about whether or not you can use contrast

A

Low kidney function

Prior reaction to contrast

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21
Q

CT contrast phases

A
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22
Q

Patient with HIV presents with symptoms constistent with kidney stone. . .

A

. . . think Indinavir!

Indivinavir can create radiolucent stones that cannot be visualized on X-ray or CT

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23
Q

Thinking about gravity in evaluating a scan for kidney stone

A

If it falls with gravity, it isn’t stuck!

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24
Q

Metformin and contrast

A

Metformin should be stopped for 48 hours after receiving contrast until creatinine has returned to normal.

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25
Q

How long after contrast administration does it take for CIN to occur?

A

3-6 days

26
Q

Azotemic renovascular disease

A

Renal insufficiency caused by decreased renal circulation, e.g., by RAS. The ischemia may cause the kidney to become small.

27
Q

Five vessel level of the thorax

A

Above the aortic arch

The trachea and esophagus are visible

  • R: R brachiocephalic vein
  • L: L brachiocephalic vein
  • I: Innominate artery/brachiocephalic artery
  • C: Left common carotid artery
  • S: Subclavian artery
28
Q

Main pulmonary artery level of the thorax

A
  • MPA: Main pulm artery
  • LB: L mainstem bronchus
  • RB: R mainstem bronchus
  • S: Superior vena cava
  • BI: Bronchus intermedius (distal to takeoff of RUL bronchus)
29
Q

High cardiac level of the thorax

A
30
Q

Low cardiac level of the thorax

A

Note that the RV has a thinner wall and is more heavily trabeculated

31
Q

The ascending aorta usually measures __ in diameter and the descending aorta is slightly smaller at __

A

The ascending aorta usually measures 2.5 to 3.5 cm in diameter and the descending aorta is slightly smaller at 2 to 3 cm.

32
Q

Aortopulmonary window level of the thorax

A

The structures here are simple, but it is important to check this window because this is the level at which enlarged mediastinal lymph nodes appear.

This level can be easily found by finding the carina and going slightly up.

33
Q

Calcium scoring on CT

A

Based on the premise that the calcium detectable in coronaries on CT correlates to the risk of heart attack.

The absence of any calcium has a high NPV against significant luminal narrowing of the coronaries.

34
Q

LAD and LCX on coronary CT angiography

A

The left coronary artery (LCA) arises from the left coronary cusp at the aortic valve.

35
Q

RCA on coronary CT angiography

A

The right aortic sinus gives rise to the right coronary artery (RCA), which courses between the right atrium and right ventricle to the inferior part of the septum

In most people, as here, the RCA continues to the posterior descending artery (right dominant circulation). In some people, the LCX gives rise to this artery (left dominant circulation). If both contribute, it is codominant.

Those w/ left dominant circulation are at increased risk for MI.

36
Q

Triple rule out scan

A

In the case of a patient with acute chest pain of uncertain etiology

An emergent CT protocol that allows for simultaneous evaluation of CAD, aortic dissection, and PE.

37
Q

What is going on in this chest CT?

A

This is nonspecific interstitial pneumonia

It is usually associated with connective tissue diseases that have lung involvement (sarcoid, myosidites, scleroderma, etc)

Imaging diagnosis is made on CT scans of the chest where basilar “ ground-glass” opacities are present and traction bronchiectasis is seen in advanced cases

38
Q

What is going on in this chest CT?

A

This is usual interstitial pneumonia

Variety of causes. Fine, reticular pattern along lobules, especially at the periphery and bases of the lung. As it progresses, honeycomb lung develops.

Imaging diagnosis is made on CT scans of the chest where honeycombing, subpleural reticular opacities and traction bronchiectasis are present, especially at the lung bases

39
Q

An important example of a disease that may present with both reticular and nodular interstitial patterns

A

Pulmonary tuberculosis

40
Q

Obesity as a contraindication to CT

A

If >300 lb, a CT may not be possible.

41
Q

Ways to reduce the potential toxicity of iodinated contrast

A
  • Pre-scan hydration
  • Post-scan hydration
  • Using a lower dose of contrast
42
Q

Three main signs of pulmonary embolism on imaging

A
  • Hampton’s hump (opacified wedge)
  • Westermark’s sign (focally absent vasculature)
  • Knuckle’s sign (prominent central pulmonary artery)
43
Q

Identify the three forms of emphysema on CT

A
  • A: Centriacinar (smoke exposure)
  • B: Panacinar (alpha-1 antitrypsin deficiency)
  • C: Paraseptal (effectively pulmonary bullae, amy cause spontaneous pneumothorax. Associated with Marfanoid body habitus)
44
Q

Pulmonary bullae

A
  • Air sacs > 1 cm in diameter in the lung
  • Usually associated with emphysema or marfanoid body habitus
  • They may grow to fill the entire hemithorax (vanishing lung syndrome)
45
Q

Wall thickness in bullae vs pulmonary cysts vs cavities

A

Bullae: < 1 mm

Pulmonary cysts: 1-3 mm

Cavities: 3 mm - centimeters

46
Q

What is the best timepoint for viewing liver metastases in a contrast CT study?

A

Portal venous phase

Since that is where the liver gets most of its blood supply!

47
Q

Metformin and CT contrast

A

Metformin should be held in patients with kidney dysfunction for 48 hours prior to a study

For patients on metformin with normal kidney function, there is no need to hold it.

48
Q

One part of the liver with a supplemental blood supply

A

The pericholecystic portion

This receives supply from the cystic artery

Hence, it is partially spared in fatty liver disease.

49
Q

What is the best way to distinguish ileus and SBO on a KUB?

A

The features of air-fluid levels

In ileus, they will be all at the same level within one loop. There will also be absent bowel sounds on exam.

In SBO, they will be at different levels within the same or multiple loops (shown). There will also be high-pitched, tinkling bowel sounds on exam.

50
Q

Apple core sign on CT

A

Can be seen on both barium enema and CT

Of course, if you use CT, you also see nodal and extraluminal disease

51
Q

A nearly or completely obstructing rectal mass . . .

A

. . . often requires urgent surgical intervention

52
Q

Rectal malignancy location and site of metastasis

A

Malignancy in the upper 2/3 of the rectum will always metastasize via the portal system

However, malignancy in the lower 1/3 of the rectum may metastasize via the portal system or the systemic venous system

53
Q

At what age do we typically stop screening for colorectal cancer?

A

Age 85

Potentially sooner depending upon health status otherwise

54
Q

A patient with newly diagnosed rectal cancer is found to also have pulmonary hilar lymphadenopathy on CT. What is the next best step?

A

FDG PET scan to determine if the hilar lymphadenopathy is due to malignant disease and screen for other metastases

When the lungs are involved, FDG PET scan should precede interventional diagnostic techniques (ie, endobronchial biopsy)

55
Q

Four categories of tumor response to chemotherapy

A
  1. Complete response
  2. Partial response
  3. Stable disease
  4. Progressive disease
56
Q

When do we give oral contrast?

A

Note: For IBD we give fluid-density contrast, not bright contrast! This helps us see the wall of the bowel better. Also called Volumen or “negative oral prep”

57
Q

When do you use isoosmolar contrast?

A

When the patient needs contrast but has a reduced renal function (GFR < 45)

58
Q

Complications to look for in diverticulitis

A
  • Abscess
  • Septic pelvic thrombophlebitis
  • Fistula
59
Q

Portal venous gas in the liver

A
60
Q

Identify these structures

A
  1. Ascending aorta
  2. Pulmonary artery
  3. Right atrium
  4. Left atrium
  5. Right ventricle
  6. Left ventricle
61
Q

If you see coffee bean sign on KUB, and the patient is stable enough to not go straight to the OR. . .

A

. . . they should get a CT to better assess the anatomy. They may be eligible for endoscopic detorsion if it is favorable.

Also note. . . it’s not always a perfect coffee bean.

Radiology Clerkship (24 decks)

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