Basics of CT interpretation

Question 1

Chest CT window interpretation

Answer 1

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

Question 2

Abdominal CT window interpretation

Answer 2

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

Question 3

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

Answer 3

Short axis of 10 mm

Question 4

Cutoff for abnormally enlarged aorta and pulmonary artery

Answer 4

• Aorta: 40 mm
• Pulmonary artery: 30 mm

Question 5

Mixing artifact

Question 6

Rim enhancing mass on CT

Answer 6

Concerning for malingnancy/abnormality

Question 7

When do you NOT use contrast?

Answer 7

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

Bones

Extravasated blood

Stones

Question 8

Types of oral contrast

Answer 8

Question 9

Barium peritonitis

Answer 9

Peritonitis caused by barium contrast irritation of the peritoneum

Question 10

When do we use volumen?

Answer 10

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

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

Question 11

Indications for oral contrast

Answer 11

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

Question 12

Indications for rectal contrast

Answer 12

Question 13

Indications for contrast cystogram

Answer 13

Question 14

Contrast reactions have greatly reduced since . . .

Answer 14

. . . we stopped using high osmolar contrast

Question 15

Allergic-like contrast reaction

Answer 15

Epinephrine!!! (if airway is at risk)

Question 16

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

Answer 16

You can premedicate with steroids and benedryl to reduce risk.

Question 17

Contrast extravasation

Answer 17

Effectively contrast-induced compartment syndrome

Question 18

Contrast induced nephropathy

Answer 18

Question 19

Preventing CIN

Answer 19

• Use iso-osmolar contrast
• Preload with fluids

Question 20

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

Answer 20

Low kidney function

Prior reaction to contrast

Question 21

CT contrast phases

Answer 21

Question 22

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

Answer 22

. . . think Indinavir!

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

Question 23

Thinking about gravity in evaluating a scan for kidney stone

Answer 23

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

Question 24

Metformin and contrast

Answer 24

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

Question 25

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

Answer 25

3-6 days

Question 26

Azotemic renovascular disease

Answer 26

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

Question 27

Five vessel level of the thorax

Answer 27

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

Question 28

Main pulmonary artery level of the thorax

Answer 28

* 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)

Question 29

High cardiac level of the thorax

Answer 29

Question 30

Low cardiac level of the thorax

Answer 30

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

Question 31

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

Answer 31

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.**

Question 32

Aortopulmonary window level of the thorax

Answer 32

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.

Question 33

Calcium scoring on CT

Answer 33

Based on the premise that the calcium detectable in coronaries on CT correlates to the risk of heart attack. ## Footnote **The absence of any calcium has a high NPV against significant luminal narrowing of the coronaries.**

Question 34

LAD and LCX on coronary CT angiography

Answer 34

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

Question 35

RCA on coronary CT angiography

Answer 35

**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.

Question 36

Triple rule out scan

Answer 36

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.**

Question 37

What is going on in this chest CT?

Answer 37

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

Question 38

What is going on in this chest CT?

Answer 38

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

Question 39

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

Answer 39

Pulmonary tuberculosis

Question 40

Obesity as a contraindication to CT

Answer 40

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

Question 41

Ways to reduce the potential toxicity of iodinated contrast

Answer 41

* Pre-scan hydration * Post-scan hydration * Using a lower dose of contrast

Question 42

Three main signs of pulmonary embolism on imaging

Answer 42

* Hampton's hump (opacified wedge) * Westermark's sign (focally absent vasculature) * Knuckle's sign (prominent central pulmonary artery)

Question 43

Identify the three forms of emphysema on CT

Answer 43

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

Question 44

Pulmonary bullae

Answer 44

* **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**)

Question 45

Wall thickness in bullae vs pulmonary cysts vs cavities

Answer 45

Bullae: \< 1 mm Pulmonary cysts: 1-3 mm Cavities: 3 mm - centimeters

Question 46

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

Answer 46

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

Question 47

Metformin and CT contrast

Answer 47

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.

Question 48

One part of the liver with a supplemental blood supply

Answer 48

The pericholecystic portion This receives supply from the cystic artery Hence, it is partially spared in fatty liver disease.

Question 49

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

Answer 49

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.

Question 50

Apple core sign on CT

Answer 50

Can be seen on both barium enema and CT Of course, if you use CT, you also see nodal and extraluminal disease

Question 51

A nearly or completely obstructing rectal mass . . .

Answer 51

. . . **often requires *urgent* surgical intervention**

Question 52

Rectal malignancy location and site of metastasis

Answer 52

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

Question 53

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

Answer 53

Age 85 Potentially sooner depending upon health status otherwise

Question 54

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

Answer 54

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)

Question 55

Four categories of tumor response to chemotherapy

Answer 55

1. Complete response 2. Partial response 3. Stable disease 4. Progressive disease

Question 56

When *do* we give oral contrast?

Answer 56

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"

Question 57

When do you use isoosmolar contrast?

Answer 57

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

Question 58

Complications to look for in diverticulitis

Answer 58

* Abscess * Septic pelvic thrombophlebitis * Fistula

Question 59

Portal venous gas in the liver

Answer 59

Question 60

Identify these structures

Answer 60

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

Question 61

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

Answer 61

. . . **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.