On the chest radiograph, constrictive pericarditis may be suggested by the presence of pericardial calcification. The calcium may be quite thin and linear and appear as “eggshell calcification” around the margins of the heart (Figure 1 A and B). Care must be taken to differentiate this pattern from the calcifications within the myocardium in old infarcts. The etiology of the pericardial calcifications in constriction is speculative, but it is seen mainly after viral and uremic pericarditis. A second type of pericardial calcification is a shaggy, thick, and amorphous deposition, which historically was rather specific for tuberculosis (Figure 2 A and B). The calcium is particularly obvious in regions of the heart in which normal fat is found, namely in the atrioventricular grooves. Calcium in the atrioventricular region may indent the heart focally, producing “extrinsic” tricuspid and mitral stenoses. However, a calcified pericardium does not necessarily imply that constriction exists.
The dense or hyperdense MCA sign refers to the appearance of the middle cerebral artery (MCA) on CT. It has been associated with poor outcome.
There is increased attenuation of the proximal portion of the MCA and it is often associated with thrombosis of the M1 MCA segment. It is one of the early signs of ischaemic stroke: MCA infarct.
The same pathological process can give an MCA dot sign when seen end on.
The sign is typically seen within 90 minutes of the ischemic event, and thus, it is very important for radiologists to recognize this sign. It can save the patient in 'golden hour' of thrombolysis (3 hours for intravenous tPA, and 6 hours for intra-arterial thrombolysis). This sign has approx. 100% sensitivity, however only 30% specificity.
It is usually associated with another important sign of acute ischaemia-insular ribbon sign.
Identification of the dense artery sign is often based on subjective interpretation and false positives may occur. One study aiming to define criteria for the sign determined that measuring Hounsfield units on the CT scan could differentiate between the dense MCA sign associated with ischemic stroke and that caused by false positives. Specifically, the combination of greater than 43 Hounsfield units and an MCA ratio of greater than 1.2 was diagnostic of a dense MCA sign associated with acute ischemic stroke.
There are occasional reports of a hyperdense MCA sign seen with HSV encephalitis
False-positives: (asymptomatic patients-usually bilateral):
The loss of the insular ribbon sign refers to a loss of definition of the gray-white interface in the lateral margin of the insular cortex ("insular ribbon") and is considered an early CT sign of MCA infarction.
The insular cortex is more susceptible to ischaemia following MCA occlusion than other portions of the MCA territory because it has the least potential for collateral supply from the anterior cerebral and posterior cerebral arteries.
In the above image the cortex of the left insular ribbon is not visualized (arrow), which is known as loss of the insular ribbon sign.
WHO criteria for diagnosing Hepatocellular carcinoma includes:
1. Alpha-foetoprotein (AFP)
2. Triphasic CT scan is the gold standard investigation
Four Phases of CT scan:
The four phases are pre contrast, arterial phase, portal venous phase, and delayed phase. Multiphase liver CT is used to detect and characterise liver lesions as different types of tumours enhance differently during each phase depending on whether they are hypervascular or hypovascular lesions.
Precontrast liver scans are used to detect calcifications, visualise haemorrhage from trauma, and demonstrate hypervascular lesions which appear hypodense compared to the surrounding liver parenchyma.
Arterial phase of scanning is performed approximately 30 seconds after the contrast injection is initiated and is most accurately detemined by using bolus tracking software (eg SmartPrep) to monitor the level of contrast enhancement in the aorta and automatically triggering the scan when it reaches a pre determined level of enhancement (eg 120HU). Hypervascular lesions enhance during the arterial phase and apper hyperdense. Arterial phase images are also used for pre operative evaluation of the arterial vasculature through the use of MIPs and 3D reconstructions.
Portal venous phase is performed 70-90 seconds post contrast and hypovascular lesions appear hypodense and hypervascular lesions appear isodense (same density as surrounding liver).
Delayed phase is performed 5-10 minutes post contrast and is used to further characterise lesions. Haemangiomas are slow to enhance and some HCC can appear hypodense due to rapid washout and CCC can appear hyperdense due to delayed washout.
Inverted Y shape is the characteristic appearance of calcified patent ductus arteriosus in a Chest X-ray, PA view.
Detection of calcification is important in the management.
In cases without calcification, triple ligation is done, which is a closed heart procedure and does not require cardiopulmonary bypass.
But this procedure cannot be performed if calcification is present.
A calcified ductus requires ligation and division with cardiopulmonary bypass.
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