Acute cerebral infarctions usually demonstrate hypodensity on non-contrast computed tomography (CT). However, in some cases, cerebral infarctions may appear to be isodense on imaging conducted during the subacute stage (2–3 weeks after onset). This phenomenon was previously called the fogging effect and has also been reported in magnetic resonance imaging. It is generally reported at T2 image, but can also be observed in diffusion-weighted image (DWI). We report three cases of the fogging effect demonstrated on CT and DWI that was conducted in the subacute stage of ischemic cerebral infarcts. The fogging effect can result in incorrect judgment during the diagnosis and treatment of cerebral infarction patients in the subacute stage. Therefore, it is important that clinicians anticipate this occurrence and necessitates the development of better detection methodologies.
Hypodensity on non-contrast computed tomography (CT) is typically observed 12 to 24 hr following acute cerebral infarctions
Studies have reported the occurrence of the fogging effect to be anywhere between 10% to 54% of reported cerebral infarction cases
A 12-year-old boy presented to the emergency department at our institution with a loss of consciousness after a pedestrian accident. The patient’s Glasgow Coma Scale score at this time was 3 points.
No evidence of intracranial hemorrhage or cerebral infarction was detected on the initial non-contrast head CT (
A 61-year-old woman with a history of hypertension and hyperlipidemia presented to the emergency department with a sudden onset headache. Though alert at the visit, the patient developed a seizure for which she was sedated.
The initial non-contrast head CT scan revealed a subarachnoid hemorrhage and a subsequent cerebral digital subtraction angiography (DSA) indicated a saccular aneurysm of the left anterior inferior cerebellar artery (AICA) (
The hypodensity lesion was observed on a non-contrast head CT in the left AICA territory of cerebellar cortex 4 days post-admission (
A 25-year-old woman who presented with mental deterioration and left-sided weakness was admitted to the emergency room in our hospital. Initial non-contrast head CT and DWI scans revealed a cerebral infarction in the right temporoparietal lobe (
Hypodensity on non-contrast CT is typically observed 12 to 24 hr following acute cerebral infarctions
Becker et al.
When retrospectively reviewed, the three cases reported here conspicuously demonstrate the fogging effect on CT images and DWI. As commonly occurs in clinical practice, we did not initially consider the fogging effect due to lack of awareness, and instead assumed that the disappearance of findings evidenced improvements, not only in terms of imaging but also clinically.
Therefore, it is important to be aware of the possibility of unusual changes in these imaging studies, and care should be taken not to unnecessarily discontinue or alter treatments due to temporary improvements visible on the images. In addition, continued research on imaging methods and interpretations of cerebral infarction in subacute stage might be needed.
In summary, the fogging effect is an unusual presentation in an imaging study that can lead to incorrect judgment in diagnosis and treatment in cerebral infarction patients during the subacute stage. Therefore, possible unusual changes in these imaging studies must be aware for continuous and proper treatment of patients.
No potential conflict of interest relevant to this article was reported.
Imaging studies for Case 1. (A) Day 1, non-contrast computed tomography (CT) shows no specific lesion. (B) Day 2, non-contrast CT shows hypodensity in both occipital lobes. (C) Day 2, diffusion-weighted image(DWI) shows high signal intensity. (D) Day 18, non-contrast CT shows isodensity. (E) Day 18, DWI changed to isosignal intensity. (F) Day 40, noncontrast CT changed to hypodensity.
Imaging studies for Case 2. (A, B) Day 1, non-contrast computed tomography (CT) & data acquisition system(DAS) demonstrated subarachnoid hemorrhage due to ruptured left anterior inferior cerebellar artery (AICA.) (C) Day 4, non-contrast CT shows hypodensity in the left AICA territory. (D) Day 14, non-contrast CT changed to isodensity. (E) Day 20, diffusion-weighted image confirmed to isosignal intensity. (F) After 1 year, DAS demonstrated blocked AICA distal flow.
Imaging studies for Case 3. (A) Day 1, non-contrast computed tomography shows hypodensity in the right temporoparietal lobe. (B) Day 1, diffusion-weighted image (DWI) shows high signal intensity. (C) Day 10, DWI changed to isosignal intensity. (D) After 4 months, DWI shows low signal intensity.