Cephaloscopic CT is the most commonly used test to screen for various neurological disorders in the emergency setting, and approximately 1 in 14 emergency patients have undergone cranial CT. However, there are many other signs of cranial CT that are easily overlooked and missed in the emergency setting. A recently published review summarizes the signs of cranial CT that are easily missed by emergency physicians in the clinical setting, with the hope that this will help clinicians in their diagnosis and treatment.
1. Middle cerebral artery hyperintensity sign
High-density middle cerebral artery sign (HMCAS) is a highly specific sign indicating middle cerebral artery (MCA) thrombosis, which is seen in 35%-50% of patients with confirmed MCA occlusion. One possible missed diagnosis is distal MCA occlusion, as the M2 segment may appear only slightly dense and hidden in the lateral fissure pool (Figure 1). Therefore, when detecting HMCAS, the entire MCA segment needs to be visualized, sometimes even in thin section.
Plain and enhanced CT shows distal MCA occlusion. (A) Focal high-density shadow in the right MCA-M2 segment and hidden in the lateral fissure pool; (B) low-density foci in the right inferior frontal gyrus, indicating recent infarction; (C) CT-enhanced angiography showing filling defects in the right M2 segment, corresponding to the high-density and low-density shadows in A and B images.
2. Brain parenchymal abnormalities
The size of ischemic foci detected on the first CT scan within 48 hours of stroke onset is positively correlated with the degree of neurological deficits at 1 week and 3 months after stroke, whereas positive CT signs at ultra-early stages (<4 hours) may indicate hemorrhagic transformation and risk of brain injury. Misclassification may occur in the presence of old infarcts, and review of previous CT findings is essential to determine old and new infarcts (Figure 2).
Figure 2. 71-year-old male patient with a previous infarction in the medial division of the anterior and middle cerebral arteries and new left-sided limb weakness. (A) Previous CT showed a focal hypointense shadow in the right frontal lobe; (B) a new cranial CT at this visit showed a larger area of poorly demarcated gray and white matter, suspected to be a new infarct; (C) DWI confirmed the new infarct.
Comparison of the existing CT with the previous CT is critical to identify whether the mild hypointensity is a new acute infarction (Figure 3).
Figure 3. 63-year-old male patient with sudden onset of acute right-sided limb weakness. (A) Previous CT shows age-related brain changes; (B) new cranial CT
shows asymmetric hypodensity in the left radiocoronal region; (C) DWI confirms left corticospinal tract infarction.
In addition, too wide or too narrow a window width on CT can miss information of diagnostic value. Therefore, adjusting the window width may improve the detection of parenchymal disease (Figure 4) and increase the proportion of acute ischemic strokes detected by emergency physicians using plain CT (Figure 5). In younger patients, the presence of indistinct gray-white matter, gray matter swelling, and shallow sulci needs to be clarified (Figures 6 and 7).
Figure 7. 41-year-old female with sudden onset of slurred speech. (A) CT scan shows slight gray-white matter border indistinctness in the left parietal lobe; (B) CT enhancement shows hypointense infarct area with vascular enhancement.
3.Traumatic cerebral hemorrhage
The density of CT imaging of subdural hematoma varies in different periods of time and generally decreases after the acute phase, which can be confused with the adjacent brain tissue or skull with similar density. Therefore, similar to stroke patients, it is important to adjust the window width to not miss abnormal signs (Figure 8). It is also important to compare previous CTs to clarify whether a new hematoma is present or to identify acute, chronic, or subacute hematomas (Figure 9).
Figure 9. 53-year-old male with a history of previous subdural hematoma who presented with an acute fall. (A) Previous CT shows a crescentic hypodense lesion, probably due to a chronic subdural hematoma; (B, C) new cranial CT at this visit shows a new hypodense foci at the left subdural hematoma, suggesting a chronic phase hematoma superimposed on an acute hematoma; (D) follow-up CT shows a high density, confirming a chronic phase hematoma superimposed on an acute hematoma.
4. Traumatic skull fracture
The orbital floor is a very thin layer of tissue that may be blinded during standard axial imaging, and fractures that are parallel or slightly oblique to the scan plane are difficult to detect, so multiplanar imaging is required to clarify the presence of fractures (Figure 10). The more easily detected secondary signs may help the physician to evaluate the proximal tissue, especially in the presence of venous sinus/papillary hemorrhage or effusion at the time of trauma (Figure 11). A frontal lobe contusion suggests the presence of a contralateral injury and needs to be examined for contralateral fractures (Figure 12).
Figure 10. 45-year-old male presented after a fall. (A) Axial CT image shows a fracture of the right orbital floor; (B, C) coronal reconstruction shows a minimal comminuted fracture of the right orbital floor.
Figure 11. Axial plain CT shows a left mastoid effusion, suggesting a left lateral temporal bone fracture.
Figure 12. 45-year-old female who fell while dancing. (A) Axial sweep CT shows a left frontal subdural hematoma and subarachnoid hemorrhage; (B, C) axial CT shows a fracture of the right occipital bone.
5. Head and neck injury
Head and neck junction injuries are not very common, but are clinically important. During initial imaging of high-speed crash survivors, cervical spine injuries may be missed, and up to 1/3 of patients may develop late neurologic symptoms. Therefore, it is important to perform a localized cranial CT examination of the patient, which may reveal minor signs that were missed (Figure 13).
Figure 13. 29-year-old patient, (A) CT localization slice showing widening of the occipito-distal space due to craniocervical dislocation; (B) CT confirmed craniocervical dislocation.
6. Headache
Headache is one of the most common symptoms in emergency patients, with approximately 3.1% of emergency patients presenting with headache. The etiology of headache is varied, and the presence of rapidly progressive parenchymal atrophy and white matter changes in the brain requires clarification of the presence of immunocompromise to aid in the diagnosis of HIV-associated encephalitis (Figure 14).
Figure 14).
Figure 14. 63-year-old male HIV patient who presented with head pain and progressively worsening delirium 2 days ago. (A) CT imaging 2 years earlier showed mild diffuse ventricular dilatation with normal brain parenchyma and white matter; (B) CT at presentation showed diffuse sulci and ventricular widening, rapid gray matter volume reduction, and hypointense white matter in the left paraventricular space; (C) MRI 3 days after presentation confirmed widespread changes in the deep white matter of the brain, consistent with HIV encephalitis; laboratory tests showed increased cerebrospinal fluid viral load with a CD4 cell count of 34; (C) MRI 3 days after presentation confirmed widespread changes in the deep white matter of the brain, consistent with HIV encephalitis. (D) coronal view showing corpus callosum involvement.
Headaches due to venous sinus thrombosis are often overlooked because they are difficult to detect on conventional plain CT. Adjusting the window width of the CT image can help detect dural sinus injury (Figure 15). labbe′ vein thrombosis, which usually results in headache and epilepsy, requires special attention because it can be confused with a focal subdural hematoma, and orthogonal reconstruction imaging can help identify it (Figure 16).
Figure 15. 51-year-old male presenting with severe headache. (A, B) Plain CT shows a high-density image of the dural venous sinus; (C, D) a subdural window is used to better visualize venous sinus thrombosis. (E) MRV imaging shows thrombosis of the right transverse sinus; (F) compression lipid image MRI imaging shows a corresponding filling defect.
Figure 16. 44-year-old male with previous history of migraine presented with altered state of consciousness. (A) Axial sweep CT shows high-density shadowing of the transverse and sigmoid sinuses, similar to a subdural hematoma; (B) sagittal sweep CT shows high-density shadowing of the left Labbe′ vein; (C) axial sweep CT shows hypointense brain parenchyma and swelling of the left temporal lobe; (D) coronal CT imaging shows a Labbe′ vein thrombosis.
Tumors are also an etiology of headache. Due to the complex structure of the midline, a careful search of the midline can be beneficial in detecting tumor lesions that may have been overlooked. One such tumor is a collagenous cyst, which accounts for 1% of primary brain tumors and usually causes severe headache in the upright position, which is relieved by lying at rest; the CT image is usually slightly denser than the parenchyma, but may also be a hypodense or isodense lesion (Figure 17).
Figure 17. 45-year-old male presenting with headache. (A) shows a round, high-density lesion in a midline location with mild dilatation of the lateral ventricles; (B, C) T2 and enhanced T1 images confirm a nonenhancing colloid cyst.
A pituitary stroke is an infarction or hemorrhage of the pituitary gland, usually in the setting of a pituitary adenoma; this patient needs to be diagnosed promptly because it progresses rapidly and may lead to coma or death. a high-density shadow in the pituitary fossa and uneven density on CT suggest the possibility of pituitary stroke (Figure 18).
Figure 18. 30-year-old female presented with headache and blurred vision. (A, B) Axial and sagittal CT scan shows enlarged pituitary gland with linear hyperdensity, suggesting hemorrhage or calcification; (C, D) axial and sagittal T1 images confirm pituitary hemorrhage.
7.Altered state of consciousness
There are many causes of altered consciousness, and careful review of previous imaging and clinical history is required. Evaluation of previous images is particularly important, especially in patients with any degree of traffic hydrocephalus with diffuse ventricular dilatation and loss of the sulcus. In patients with a known history of tumor, the presence of these signs may suggest carcinomatous meningitis (Figure 19).
Figure 19. 59-year-old female with a previous history of metastatic breast cancer presented with a decreased level of consciousness. (A) previous axial T2-Flair image showed no abnormality; (B) admission plain CT showed diffuse ventricular dilatation and loss of sulci, suspicious of traffic hydrocephalus; ( C, D) enhanced T1 image showed soft meningeal enhancement and ventricular dilatation, suggestive of soft meningeal carcinoma metastasis, a diagnosis subsequently confirmed by cerebrospinal fluid test results.
Toxic or metabolic disease may result in bilateral or symmetrical lesions, and metabolic etiologies usually involve the basal ganglia. The differential diagnosis of bilateral pallidum abnormalities includes ischemic-hypoxic encephalopathy, carbon monoxide poisoning, substance abuse, sequelae of liver failure, and drug injury. In this patient (Figure 20), the pallid bulb lesions suggest the possibility of acute carbon monoxide poisoning, which requires early diagnosis and treatment.
Figure 20. 51-year-old patient with a history of previous substance abuse. Presented to the clinic with an acute altered state of consciousness. (A) previous plain CT did not show any abnormality; (B) at the time of presentation, CT plain showed bilateral pallid bulb hypodensity suggesting necrotic changes; loss of diffuse sulci and ventricular narrowing suggested mild diffuse cerebral edema (C) DWI confirmed the pallid bulb lesion, and subsequent findings suggested acute elevated blood ammonia levels.
Conclusion
This article lists life-threatening and time-sensitive diseases, and emergency plain CT is highly likely to miss key imaging features of these diseases. It is a challenge for emergency physicians to identify these signs in a timely, accurate, and effective manner in an emergency setting, and the key to minimizing the rate of missed diagnoses is to master these easily missed but critical signs.
The cranial CT imaging features of acute ischemic cerebral infarction include.
A poorly defined gray and white matter and swelling of the gray matter;
B shallowing of the cerebral sulcus, disappearance of the cerebral sulcus, and blurring of the caudate nucleus head;
C the presence of high density sign of middle cerebral artery;
D All of the above are correct.