A lucency on a plain film, which appears as a region of decreased density, corresponds to a hypodense region on a computed tomography (CT) scan. Hypodense areas on CT scans are characterized by lower Hounsfield units (HU) compared to surrounding tissues, appearing darker on the grayscale image.
Clinical implications of hypodense regions on CT scans
- Traumatic brain injury: Hypodense lesions identified on CT scans after severe traumatic brain injury do not always indicate ischemia. The regional cerebral blood flow (rCBF) in these hypodense areas can be variable. The cause of the lesion is a major factor associated with the level of rCBF. For instance, hypodense regions associated with contusions often have a significantly lower rCBF compared to those associated with infarctions
- Intracerebral hemorrhage: Hypodensities on noncontrast CT scans can help predict hematoma growth in patients with intracerebral hemorrhage, although the predictive values are not very satisfying
- Pulmonary infarction: In the context of pulmonary infarction, CT images with infarct have a higher frequency of central lucencies, which are hypodense areas
In conclusion, a lucency on a plain film would appear as a hypodense region on a CT scan. The clinical implications of these hypodense regions can vary depending on the context, such as in traumatic brain injury, intracerebral hemorrhage, and pulmonary infarction.