Identifying a unilateral hemorrhage within the brain on a computed tomography (CT) scan is not particularly difficult. Determination of the cause is more difficult—but is essential for planning appropriate treatment and follow-up.
In weighing the probable causes of a unilateral hemorrhage, one should consider the following factors:
- Medical history
- Hemorrhage location
- Evidence or history of drug use
- Patient’s age
When considering the cause of unilateral hemorrhage, a patient’s age is a good starting point. For example, a basal ganglia hemorrhage in a premature newborn usually arises from immature vessels in the germinal matrix, while the most common cause of hemorrhaging in the basal ganglia among middle-aged and older adults is chronic hypertension.
In patients over 75 years of age, hemorrhaging is frequently due to an underlying condition common with aging called amyloid angiopathy. Thoughtful use of CT angiography (CTA), CT venography (CTV), magnetic resonance imaging (MRI), contrast, and in some cases, digital subtraction angiography (DSA) are typically used to establish the diagnosis.
Parenchymal hemorrhage case 1: Brain infection
While chronic hypertension may lead to a basal ganglia hemorrhage, you cannot be certain about the cause of a hemorrhage based only on its location. You should follow the approach used by Sherlock Holmes—examine all the evidence before reaching any conclusions!
In our first case, an initial non-contrast CT scan was obtained immediately after symptom onset in an immunocompromised patient and revealed a hemorrhage surrounded by low attenuation, suggesting peripheral edema. This finding, along with the location of the hemorrhage, and the patient’s history led to an investigation for an underlying cause. The hemorrhage proved to be due to a brain infection with aspergillus.
But, a hemorrhage surrounded by edema is not a reliable sign of infection. This finding normally appears in the days after any hemorrhage, as a reaction to the evolving blood products.
Parenchymal hemorrhage case 2 and 3: Arteriovenous malformation
In our second case, a 30-year-old patient presented with left-sided hemiparesis with no history of hypertension or drug use. This patient’s CTA demonstrated a cluster of enhancing blood vessels near the hemorrhage consistent with an arteriovenous malformation (AVM).
A DSA confirmed this diagnosis on the carotid injection where a large, early draining vein was demonstrated arising from the dense nidus of the AVM. Notice that no other veins were visible on this angiogram image taken in the early arterial phase which established that this is an early vein, characteristic of an abnormal arteriovenous communication within the AVM.
After a 42-year-old patient presented with an acute onset of a seizure, their non-contrast CT in the emergency room (ER) demonstrated a left temporal lobe hemorrhage. There was no history of trauma or hypertension in this case.
A CTA was also obtained in the ER, which showed abnormal enhancement at the periphery of the hemorrhage. This finding (although less obvious compared to the previous case) suggested an AVM as the source of the parenchymal hemorrhage.
The DSA with injection of the left carotid demonstrated an enlarged supplying artery to a small cluster of vessels (called a nidus), and the early draining vein which is characteristic for an AVM.
Parenchymal hemorrhage case 4: Links to medication use
The fourth case involves a 20-year-old woman who recently started birth control pills and presented with new seizures and aphasia. Her CT demonstrated a left temporal lobe hemorrhage. Based on her age and history, a CTA was ordered.
When examining the CTA, you may be looking for abnormal vessels near the hemorrhage after the past two cases, but the problem here does not lie in the arterial system. The patient had a thrombus in the left sigmoid sinus that extended to involve the left vein of Labbé.
The vein of Labbé drains the lateral temporal lobe. The loss of normal venous drainage of the left temporal lobe led to venous hypertension with a resultant parenchymal hemorrhage in this patient.
Parenchymal hemorrhage case 5: Venous occlusion
In our fifth case, a computed tomography venography (CTV) demonstrated a clot in the superior sagittal sinus. On enhanced imaging, this is called the empty delta sign. A CTV is a variation of a CTA where the brain is scanned slightly later to show enhancement of the veins instead of the arteries.
Additional testing for suspected venous occlusion
In cases where you suspect venous occlusion based on symptoms or history, look carefully at the large venous structures on non-contrast CT. Just as we saw in the arteries, clotted blood has a higher attenuation than normal flowing blood. However, diffuse venous occlusion is possible, so you cannot rely on comparing the appearance of veins side to side.
If you measure the attenuation of a venous sinus using picture archiving and communications system (PACS) tools on a computer and it is above 70 HU, this suggests a venous occlusion. However, whenever venous occlusion is suspected, it should be confirmed on an MRI or CTV. This is because values below 70 HU in the sinuses do not ensure that the veins are normal, and values of 70 HU and above are possible in patients with polycythemia since attenuation follows the patient’s hematocrit.
In many cases, the cause of a venous occlusion cannot be confidently established. When the cause of a venous thrombosis can be identified, it is often the result of one of the following five possibilities:
- Inherited clotting disorders
- Drugs (including birth control pills)
- Hypercoagulation (in patients with cancer)
Parenchymal hemorrhage case 6 and 7: Chronic hypertension
In our sixth case, chronic hypertension was determined to be the cause of a patient’s left basal ganglia hemorrhage since the patient had a long history of poorly controlled hypertension. The patient’s high attenuation hemorrhage was not surrounded by low attenuation edema and appeared uniform. This is typical for a benign hemorrhage and argues against hemorrhage into an underlying tumor.
The next case involves a 68-year-old man who presented to the ER with a sudden loss of balance and headaches. The CT scan demonstrated a cerebellar hemorrhage resulting in mass effect. He had a history of hypertension and a systolic blood pressure of 220 mmHg in the ER.
A susceptibility-weighted MRI was obtained immediately after the CT at the time of his presentation. It demonstrated multiple areas of signal loss elsewhere in the brain. This finding indicated the presence of prior hemorrhages (likely subclinical) that were predominantly in the basal ganglia. This is a typical pattern for microbleeds in patients with chronic hypertension, which was most likely the cause of his cerebellar hemorrhage.
Be aware that after an acute intracranial hemorrhage, some patients will have elevated blood pressure. The observation of high blood pressure alone should not be used to establish the diagnosis of a hypertensive hemorrhage since they are usually the result of years of poorly controlled hypertension.
Parenchymal hemorrhage case 8: Amyloid angiography
When an 82-year-old patient presented with confusion and headache to the ER, his CT scan demonstrated a large frontal lobe hemorrhage. An MRI was ordered to determine whether this was from a hemorrhagic infarction, an underlying tumor, or an amyloid angiography.
Susceptibility-weighted MRI scans are extremely sensitive to the presence of blood products within the brain. On this patient’s susceptibility-weighted scan, you can see innumerable small dots from susceptibility effects of blood products, but with much less involvement of the basal ganglia than the last patient. This pattern on susceptibility-weighted imaging in a patient over 70 years of age strongly supports the diagnosis of amyloid angiography. In this case, it was the most likely cause of the hemorrhage.
While the finding of innumerable small dots on an MR susceptibility-weighted scan indicates amyloid angiopathy in a patient over 75, in a 30-year-old it would suggest underlying vasculitis. Always keep the age and clinical context in mind as you review imaging for patients with parenchymal hemorrhages!
Parenchymal hemorrhage case 9: Drug use
A 50-year-old patient presented with a cortical hemorrhage, a subcortical hemorrhage, and elevated blood pressure. While a hemorrhagic infarction or cortical vein occlusion is a possibility with this appearance, his drug screen in the ER was positive for cocaine and he admitted to using cocaine just before the onset of symptoms. Drugs like cocaine, methamphetamine, and others may sharply elevate blood pressure and should be considered in all patients with an acute brain hemorrhage.
Parenchymal hemorrhage case 10: Brain tumor
In our tenth case, a 50-year-old patient presented with a right-sided basal ganglia hemorrhage and no history of hypertension. His CTA was negative, but an MRI with contrast demonstrated enhancement at the periphery of a blood clot one day after symptom onset.
This enhancement was suspicious since benign hemorrhages should not enhance at all on the acute phase MRI, so a repeat MRI scan was obtained six weeks later. This exam showed more extensive, inhomogeneous enhancement. A needle biopsy of this lesion confirmed the diagnosis of an aggressive primary brain tumor (a glioblastoma), that was undoubtedly the source of the hemorrhage.
Keep an open mind when considering the cause of a parenchymal nontraumatic hemorrhage, since it can be the presenting sign of many diseases involving the brain. Location of the blood, such as the basal ganglia, does not establish the hemorrhagic cause in all patients.
Reaching the correct diagnosis will require you to consider the age of the patient, imaging findings, and the patient’s medical history to guide the work-up. Additional imaging beyond CT and CTA is frequently necessary to establish the cause of hemorrhaging.
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