Approaches to Interpretation of CT

Head

Prior imaging	oldest & most recent PET, MRI
Scout	Lines, tubes, #'s, C-spine
Bone window	#'s, sinuses, lesions
Brain window	mass effect, blood (esp. SDH), edema, gray-white differentiation, CSF, arteries (aneurysms, calcifications)
Soft tissue window	Vessels, LN's, salivary glands, thyroid

Chronicity of Hemorrhage

0 - 2 hrs	40 - 60 HU
3 - 48 hrs	60 - 80 HU
3 - 7 days	hyperdense core surrounded by hypodense halo
> 2 wks	hypodense

Edema

Vasogenic:
Due to increased permeability of brain capillary endothelial cells to plasma proteins. Greatest in white matter. Astrocytes become swollen.

E.g. trauma, tumors, focal inflammation, and late stages of cerebral ischemia.

Cytotoxic:
Characterized by swelling of all the cellular elements of the brain. In the presence of acute cerebral ischemia, neurons, glia, and endothelial cells swell within minutes due to failure of ATP-dependent ion (sodium and calcium) transport. With the rapid accumulation of sodium within cells, water follows to maintain osmotic equilibrium. Increased intracellular calcium activates phospholipases and the release of arachidonic acid, leading to the release of oxygen-derived free radicals, and infarction.

E.g. various intoxications (dinitrophenol, triethyltin, hexachlorophene, isoniazid), Reye's syndrome, severe hypothermia, and early ischemia.

Spine

Critical spinal stenosis, AP dimension of thecal sac:
1.0 cm
1.4 cm in L-spine

Chest

Prior imaging	oldest & most recent PET, MRI
Scout	Lines, tubes
Lung window	Airways: endobronch lesns bronchial wall thickening (wall thickness > diameter adjacent vessels) bronchiectasis (cylindrical, varicose, cystic) Lung parenchyma: emphysema (centrilobular, paraseptal, panlobular) bulla > 1 cm
Soft tissue window	Flow of contrast, heart, great vessels, LN's Abd (ascites, free air, vessels, adrenals, kidneys, spleen, pancreas)
Liver window	Liver (density, lesions, cirrhosis)
Bone window	Lines, #'s, lesions, invasn

Normal	Else
Main PA < 3 cm	Indicative of PA hypertension
Aorta: Root < 3.6 cm Ascending < 3.5 cm Proximal descending < 2.6 cm Distal descending < 2.4 cm Abd < 3 cm	Aneurysm If < 4 cm → ectasia If > 4 cm → dilatation

Density > 200 HU indicates calcification

Cavity wall thickness:
< 2 mm, 95% benign
2 - 15 mm, 50% malignant
> 15 mm, > 95% malignant

Eccentric cavity or shaggy internal margins suggests malignancy.

Regional Nodal Stations for Lung Cancer Staging
_{(American Joint Committee on Cancer(AJCC) and the Union Internationale Contre le Cancer (UICC))}



1 (red) = highest mediastinal nodes
2R and 2L (dark blue) = right and left upper paratracheal nodes
4R and 4L (orange) = right and left lower paratracheal nodes
7 (blue) = subcarinal nodes
8 (grey) = para-oesophageal nodes
9 (brown) = pulmonary ligament nodes
10R and 10L (yellow) = right and left hilar nodes
11R and 11L (green) = right and left interlobar nodes
12R and 12L (pink) = right and left lobar nodes
13R and 13L (pink) = right and left segmental nodes
14R and 14L (pink) = right and left subsegmental nodes
3 (pink) = pre-vascular and retrotracheal nodes
5 (black) = subaortic nodes
6 (red) = para-aortic nodes


Fleischner Society Recommendations for Incidental Pulmonary Nodule Follow-up

Multinodular Disease: A High-Resolution CT Scan Diagnostic Algorithm

Abdomen

Prior imaging	oldest & most recent PET, MRI
Scout	Lines, tubes
Liver window	Density, lesions, cirrhosis
Soft tissue window	Skin, hernia, adrenals, kidneys, spleen, pancreas,gallbladder, LN's ureters, bladder, bowel, terminal ileum, appendix prostate, seminal vesicles, uterus, ovaries
Bone window	#'s, lesions
Lung window	Lung bases

Liver lesions

Cyst	Thin, smooth wall 0 - 15 HU No enhancement No septations
Cavernous hemangioma	Discontinuous, nodular peripheral enhancement Centripetally-filling Isodense to aorta
Adenoma	Heterogen enhancement Well-defined capsule
FNH (fibrolamellar HCC similar)	Art phase: homogen enhancement (key) Solid (isodense when unenhanced) Central scar Radiating fibrous septa Portal venous phase: ↑ periph enhancement (dt lge pariph veins [no capsule])

Bosniak classification of cystic renal masses by CT scanning

Category	Meaning	Criteria
I	Simple benign cyst	Hairline thin wall Density less than 20 HU(similar to water) No septa, calcification, or solid components No enhancement
II	Benign cyst	A few thin ( < 1 mm thick) septa No measurable enhancement (may be "perceived" enhancement) Includes uniformly high attenuation lesions <3 cm that are well marginated and do not enhance
IIF	Minimally complicated cyst that requires follow-up	Multiple hairline thin septa or minimal smooth thickening of the wall or septa No measurable enhancement (may be "perceived" enhancement) Thick and nodular calcification of the wall or septa Totally intrarenal, nonenhancing, high attenuation lesions >3 cm
III	True indeterminate cystic mass that typically undergoes surgical evaluation	Thickened wall or septa in which measurable enhancement is present
IV	Mostly malignant	Enhancing soft-tissue components adjacent to, but independent of, wall or septum

^{N.B. Enhancement = attenuation increase by at least 10 HU}

Adrenal lesions
Nl limb 4 - 9 mm

Adenoma	< 10 HU < 5 cm Sl enhancement Washout > 60%
Adenocarcinoma	usu > 5 cm Heterogen enhancement Calcifn in 30% - 50%
Metastasis	Usu bilat > 10 HU ↑ & heterogen enhancement Washout < 60%
Myelolipoma	< 0 HU

Bowel Calliber
"3 - 6 - 9 - 12"

Region	Max diameter
Small bowel	3 cm
Transverse colon	6 cm
Cecum	9 cm
Cecum b/f bursting	12 cm

Small Bowel
"Rule of 3's"

Wall thickness < 3 mm
Fold thickness < 3 mm
Diameter < 3 cm
Air-fld levels < 3

Appendicitis


Appendocicolith
Diameter > 6 mm
Wall thickness > 2 mm
Enhancing wall
Peri-appendiceal fat stranding
Peri-appendiceal fld collection

Diverticulitis


Wall thickness > 3 mm
Peri-colonic fat stranding
Peri-colonic or intramural fld collection (abscess)