ABC-Primer of CT Evaluation

Occasionally, the beginner faces the question to decide whether a finding represents a true lesion or just an artifact. A contralateral comparison or a comparison with adjacent cranial or cauda sections can often be helpful. Furthermore, uncertainty arises when describing a lesion without familiarity with the appropriate vocabulary. This primer aims to remedy these problems.

A


General Approach to an Abnormality of the CT Morphology:
Where ?	Location, lateralization, relative position to other organs/vessels
Size ?	Size (diameter in [mm, cm]; important, e.g., monitoring of therapy)
Density ?	Relative to its surrounding: isodense (equal density); hyperdense (denser); or hypodense (less dense)
Structure ?	Homogenous (e.g., fluids) or heterogenous / septate / geographic
Shape ?	Tubular (vessels, muscles, …) or nodular (tumor, lymph nodes)? Reticular (resembling a net), striate or diffuse?
Demarcation ?	Sharply marginated (more likely benign) or indistinctly marginated (infiltration into the surrounding, e.g., inflammation, malignancy) Caution: Partial volume effect can mimic an indistinct margin!
Perfusion ?	No, peripheral, homogenous or heterogenous contrast enhancement
Expansion ?	Space-occupying effect not invariably a sign of malignancy: e.g., large benign cysts can displace adjacent vessels

B


Useful Terms, in Alphabetic Order	( Application, Possible Significance)
Air inclusions	Infection with gas-forming bacteria compound fracture
Ampullary	Dilatation of the renal pelvis ( physiologic variant or obstructive uropathy)
Articular involvement	Evaluation of fractures ( risk of degenerative osteoarthritis)
Bolus CT	Dynamic examination, often without table movement to assess the contrast enhancement pattern
Bullae	Lung ( pulmonary emphysema)
Capping	Periventricular abnormality in the white matter ( transependymal diffusion of CNS; sign of SAE)
Cavity	Intrapulmonary hollow space ( tuberculosis)
Central	In the center of a lesion or close to the hilum of parenchymatous organs
Clubbing	e.g., of a limb of the adrenal gland ( adenoma, metastases)
CM	Contrast medium, given orally, rectally or intravenously
Concentric	Location of intravascular thrombi ( aortic aneurysm)
Course of fracture lines	Evaluation with additional MPR ( surgical planning)
Crescentic	Typical configuration, e.g., subdural hematoma or perihepatic effusion / ascites
Defect	Pathologic phenomenon in opacified vessels / urinary collecting system
Defect	In opacified vessels ( thrombus), in urinary bladder ( tumor, blood clot)
Demarcation	Depending on the vascularization, lesions become visible only after administration of contrast medium
Dense band	Band-like density ( lung, connective tissue: post-inflammatory, scar)
Densitometry	Measuring of density ( differential diagnosis)
Diffuse	Uniform, neither focal nor nodular; e.g., liver: hypodense hepatic steatosis (fatty liver) hyperdense hemochromatosis
Dumbbell-like	Typical calcification pattern of benign hamartomas ( lung)
Eggshell-shaped	Calcification pattern of perihilar lymph nodes (lung silicosis; porcelain gallbladder)
Enhancement	Increased density due to accumulation of contrast medium
Enhancement pattern	Perfusion pattern (homogenous, timely or delayed)
Excentric	Intravascular location of thrombi ( aortic aneurysm)
Fluid Levels	Phenomenon ( sedimented hematoma) or air-fluid levels ( paralytic ileus or intestinal obstruction)
Fractures	Cortical step deformity, displacement, number of fragments, stability, articular surface?
Ground glass density	Diffuse, slight increase density seen in perifocal edema ( fat, lung)
Halo	Confined perifocal edema ( around inflammatory foci and metastases)
Hemorrhagic	Blood-containing ( large infarcts, e.g., cerebral)
Hilar fat	Benign criterion for lymph nodes ( nodal index)
Honeycombing	Typical for vascular rarefaction in the lung ( emphysema)
HRCT	High resolution computed tomography (thin sections) ( lung; also for MPR and 3D)
Hyperdense	Denser than the surrounding tissue (bright fresh cerebral bleeding or calcification)
Hyperperfusion	Enhancement ( inflammation, hypervascular tumor)
Hypodense	Less dense than the surrounding (dark fluid, fat, air)
Imbibition	Striate to diffuse enhancement ( fatty tissue: scar, inflammation)
Indentation	Blunt convex bulging / displacement of adjacent structures ( tumors)
Indistinct	Outline of a lesion (see marginal indistinctness)
Indistinct margin	Caused by inflammatory and tumorous infiltration of the surrounding tissue (caution: DD partial volume effect)
Induration	Thickened fibrous tissue ( scar, pulmonary fibrosis)
Infiltration	Perifocal extension of an inflammatory or malignant process
Inflow effect	Incomplete mixing of contrast medium, can mimic intravascular thrombi
Intramural	Located in the wall of a hollow viscus ( gas, tumor)
Iris effect	Centripetal enhancement ( hepatic hemangiomas)
Isodense	As dense as … (= isointense)
Jet effect	Inflow of opacified urine from the ureter into the urinary bladder
Lacuna	Lacunar defect ( late stage after cerebral infarct, isointense with CSF)
LN	Lymph node (for size see checklists, hilar fat)
Lymphangiomatosis	Ground glass-density ( pulmonary parenchyma, breast carcinoma)
MPR	Multiplanar reconstruction of various image planes (sagittal, coronal diagnostic evaluation of e.g. fractures)
Multiphase technique	Data acquisition during early arterial, portovenous or late venous passage of the contrast medium bolus ( spiral CT of the liver)
Multislice	New multislice technique consisting of simultaneous acquisitions of several sections in spiral mode
Mural thickness	Single or multiple layers (wall of a hollow viscus: ischemia, inflammation)
Narrowed parenchymal rim	Renal atrophy (degenerative, hydronephrosis)
Necrosis	Central, hypodense or homogenous liquefaction
Nodal index	Longitudinal-transverse diameter ratio (characterization of lymph nodes)
Nodular	Nodular configuration ( lymph nodes, tumors, adenomas), miliary < granular < fine-nodular < large-nodular < confluent ( pulmonary interstitium)
Obliterated	Surface of cerebral gyri ( cerebral edema, DD: child) or pancreas outline ( acute pancreatitis)
Osteolytic	Destruction of bony matrix ( metastases, multiple myeloma)
Osteoproliferative	Osseous apposition ( degenerative), less frequent due to sclerotic metastases
Partial volume effect	Effect of partial volume (causes apparent indistinctness)
Patchy	Parenchymal perfusion pattern in the spleen during the early arterial phase
Perifocal	Circular around a lesion (edematous zone)
Perihilar	Topographic description of an intrapulmonary lesion
Peripheral	Along the periphery, in contrast to central
Pitch	Ratio of table feed per rotation and section thickness ( spiral technique, see p. 8 / 9)
Pixel	Picture element (image formation, see p. 14)
Plaque	Intravascular ( arteriosclerosis), pleura-based ( asbestosis)
Polycyclic	= scalloped, cauliflower-like ( hilar lymph nodes of the lung, e.g., Boeck’s disease)
Popcorn	Typical pattern of benign calcifications ( lung)
Process	Favored term for “I don’t know what is means”
Pseudocysts	chronic pancreatitis
Pulsation	Can induce artifacts along vessels ( aortic aneurysm)
Rarefaction	Less vessels per pulmonary volume ( emphysema, S/P lobectomy)
Respecting soft-tissue planes	Lacking in malignant tumors or advanced inflammations (no longer respecting natural borders => infiltration)
Retention cyst	Convex projection into the paranasal sinus, homogenous
Reticular	Net-like pattern ( fibrosis of the pulmonary interstitium)
Retrocrural	Preferred posterior paravertebral lymph node station
Risk of herniation	Internal herniation of brain stem due to increased intracranial pressure ( quadrigeminal and ambient cisterns)
ROI	Region of interest ( densitometry)
Round lesion	Focal space-occupying lesion (only intrapulmonic)
Scalloped enhancement	Peripheral contrast enhancement ( glioblastoma)
Site of predilection	Preferred site for certain changes ( lymph nodes, metastases)
Sludge	Thickened bile ( cholestasis, cholecystitis)
Space-occupying process	Tumor of unknown nature (ubiquitously applicable)
Spindle-shaped	Biconvex configuration ( aortic aneurysm; epidural hematoma)
Spiral CT	Acquisition of a 3D data set with continuous table feed and any section reconstruction, see p. 7
Stellar	Hypodense star-like figure ( FNH of the liver)
Stellate	Septation ( echinococcal cyst)
Stent	Short tube of various materials to stent vessels, ureter or common bile duct
Step deformity	bony cortex ( fracture diagnosis)
Structure	Non-descriptive term of a lesion, try to use more precise term
Subcarinal	Preferred lymph node station
Timely	Symmetric and timely renal enhancement and excretion of contrast medium = normal
Triangular	Wedge-shaped ( typical infarct pattern, scar residue)
Tumor extension	Renal vein or vena cava ( renal tumor)
Vascular configuration	Normal configuration of the pulmonary hila
Voxel	Volume element (image formation, see page 14)
Wedge-shaped	Triangular configuration ( typical infarct pattern, scar residue)