Ill-defined focal low attenuation in the posterior internal capsule: a normal CT finding.

Although many pathological changes in the internal capsule may lead to neurological deficits, we often encounter ill-defined focal low attenuation in the posterior limb of the internal capsule (PIC) on CT in patients with no neurological disturbance. Brain CT studies of 141 patients without neurological deficits were reviewed to investigate the position of the focal low attenuation by analysis of a profile density curve. Nine patients with lacunar infarcts only within the posterior internal capsule were also studied. The focal low attenuation areas were ill-defined and bilaterally symmetrical, without mass effect. They were seen consistently within the posterior limb of the posterior internal capsule. Correlation between the distribution of these foci and the position of lacunar infarcts in the posterior internal capsule in nine patients with neurological deficits suggests that they may be related to the corticospinal tract.