Approach to Nontraumatic Hemorrhage and Vascular Lesions

Main Text

Preamble

This part devoted to “spontaneous” (i.e., nontraumatic) hemorrhage and vascular lesions begins with a general discussion of brain bleeds. Subsequent chapters delineate a broad spectrum of vascular pathologies, ranging from aneurysms/subarachnoid hemorrhage and vascular malformations to cerebral vasculopathy and strokes. Where appropriate, anatomic considerations and the pathophysiology of specific disorders are included.

Spontaneous (i.e., nontraumatic) intracranial hemorrhage (sICH) and vascular brain disorders are second only to trauma as neurologic causes of death and disability. Stroke or “brain attack”—defined as sudden onset of a neurologic event—is the third leading overall cause of death in industrialized countries. Imaging plays a crucial role in the management of stroke patients, both in establishing the diagnosis and stratifying patients for subsequent treatment.

We start this chapter with a brief overview of nontraumatic ICH and vascular diseases of the CNS, beginning with a short discussion of who, why, when, and how to image these patients. We then develop an anatomy-based approach to evaluating nontraumatic ICH. We close the discussion with a pathology-based introduction to the broad spectrum of congenital and acquired vascular lesions that affect the brain.

Imaging Hemorrhage and Vascular Lesions

Who, Why, and How to Image?

Because of its widespread availability and speed, an emergent NECT scan is generally the first-line imaging procedure of choice in patients with sudden onset of an unexplained neurologic deficit.

If the initial NECT scan is negative and no neurologic deficit is apparent, further imaging is often unnecessary. However, if the history and clinical findings suggest a thromboembolic stroke or transient ischemic attack (TIA), additional imaging is indicated, typically on an emergent basis.

Imaging studies are also frequently obtained in patients with headache of any kind, often with little or no initial evaluation. The first step in the evaluation of any headache patient should be a detailed clinical history and relevant clinical examinations. The American Academy of Neurology (AAN) and the American College of Radiology (ACR) do not recommend neuroimaging for patients with primary headache in the absence of so-called red flags [i.e., subacute head trauma, related activity (sexual activity, exertion, position), neurologic deficit, known or suspected cancer, immunosuppressed or immunocompromised state, pregnancy, age ≥ 50 years].

The ACR has established consensus Appropriateness Criteria for initial imaging in patients with different clinical types of headache, including those in which neuroimaging is mandatory. A variety of conditions are considered and given one of three appropriateness categories (“Usually Appropriate,” “May Be Appropriate,” and “Usually Not Appropriate”). These are briefly summarized in the following “ACR Appropriateness Criteria: Headache” table.

If ICH is identified, or if there is also a new neurologic deficit, further imaging should be considered using consensus studies, such as the ACR Appropriateness Criteria, summarized in the following table.

ACR APPROPRIATENESS CRITERIA: HEADACHE

Variant 1: Sudden Severe Headache (“Worst Headache of Life”)

• NECT usually appropriate

• CTA may be appropriate

• CECT, MR, MRA usually not appropriate

Variant 2: New Headache With Optic Disc Edema

• NECT, MR ± contrast usually appropriate

• CTV, MRV may be appropriate

• CECT, DSA usually not appropriate

Variant 3: New/Worsening Headache With Clinical Red Flags

• NECT, MR ± contrast usually appropriate

• CECT, MRA, DSA usually not appropriate

Variant 4: New Headache (Classic Migraine/Tension-Type, Normal Neurologic Examination)

• Imaging (CT, MR, etc.) usually not appropriate

Variant 5: New Primary Headache, Suspected Trigeminal Autonomic Origin

• MR ± contrast usually appropriate

Variant 6: Chronic Headache, No New Features, No Neurologic Deficit

• Imaging (CT, MR, etc.)

Variant 7: Chronic Headache With New Features or Increasing Frequency

• MR ± contrast usually appropriate

• CT ± contrast may be appropriate

• MRA, CTA, DSA usually not appropriate

When and How to Image?

In sudden, severe headache, the negative predictive value of NECT performed with a modern scanner and obtained within the first six hours of symptoms is virtually 100% (sensitivity of 0.987 and specificity of 0.999).

Some of the most challenging questions arise when screening NECT discloses parenchymal hemorrhage. What are the potential causes? Should further emergent imaging be performed?

Spontaneous nontraumatic “brain bleeds” carry high mortality and morbidity (4-1). The risk of rapid neurologic deterioration is high (4-2). Rapid hematoma expansion and growth is common in the first few hours after onset (4-3). High-quality, emergent imaging is crucial in further evaluating and managing these patients.

CTA is indicated in patients with sudden clinical deterioration or a mixed-density hematoma (indicating rapid bleeding or coagulopathy). A spot sign with active contrast extravasation caused by rupture of a lenticulostriate microaneurysm (Charcot-Bouchard aneurysm) can sometimes be identified. Contrast extravasation in sICH predicts hematoma expansion and poor clinical outcome.

CTA is also an appropriate next step in children and young/middle-aged adults with spontaneous (nontraumatic) ICH detected on screening NECT (4-4) (4-5). In contrast to older adult patients—in whom hypertensive hemorrhage and amyloid angiopathy are the two most common etiologies of unexplained sICH—vascular malformation is the most common underlying etiology in younger age groups (4-6).

Emergency MR is rarely necessary if CTA is negative. However, follow-up MR ± contrast enhancement can be very useful in patients with unexplained ICH. In addition to the standard sequences (i.e., T1WI, T2WI, FLAIR, DWI, and T1 C+), a T2* sequence—either (or both) GRE or susceptibility-weighted imaging (SWI)—should be obtained.

MR evidence for prior hemorrhage(s) and cerebral “microbleeds” can be very helpful in narrowing the differential diagnosis. Benign ICH typically follows an orderly, predictable evolution on MR scans. MR evidence of disordered or bizarre-looking hemorrhage should raise the possibility of neoplasm, underlying arteriovenous malformation (AVM), or coagulopathy.

If MR demonstrates multiple parenchymal hemorrhages of different ages, the underlying etiology varies with patient age. Multiple microbleeds in older adult patients are typically associated with chronic hypertension or amyloid angiopathy. Cavernous malformations or hematologic disorders (4-16) are the most common causes in children and young adults.

Approach to Nontraumatic Hemorrhage

Preamble

Hematoma location, age, and number (solitary or multiple) should be noted.

The differential diagnosis of nontraumatic sICH varies widely with anatomic location and patient age. Because the brain itself is the most common site, we begin our discussion with intraaxial hematomas, then turn our attention to extraaxial bleeds.

Intraaxial Hemorrhage

Clinical Issues

Parenchymal hemorrhage is the most devastating type of stroke. Although recent advances have improved the treatment of ischemic strokes, few evidence-based treatments exist for ICH. Strategies are largely supportive, aimed at limiting further injury and preventing associated complications, such as hematoma expansion, elevated intracranial pressure, and intraventricular rupture with hydrocephalus.

Imaging

Parenchymal hematomas are easily recognized on NECT scans by their hyperdensity or, in the case of rapid bleeding or coagulopathy, mixed iso-/hyperdense appearance. Expansion of a parenchymal hematoma into the ventricular system is commonly encountered on initial imaging in patients with sICH and associated with poor long-term outcome.

Hematomas typically expand the brain, displacing the cortex outward and producing mass effect on underlying structures, such as the cerebral ventricles. The sulci are often compressed, and the overlying gyri appear expanded and flattened. The surrounding brain may appear grossly edematous.

When immediate follow-up imaging after thrombolysis for acute stroke is obtained, it is important to differentiate parenchymal hemorrhage from contrast extravasation. Both are hyperdense on NECT on standard sequences. Dual-energy CT (DECT) acquires two datasets with different x-ray energy levels from the same anatomic region. Blended images are generated through a combination of the acquired low-energy (80-kilovoltage peak [kVp]) and high-energy (150-kVp) datasets to simulate a standard 120-kVp dataset. Virtual nonenhanced images can be generated using this dual-energy technique and may help differentiate contrast staining from true ICH (4-7).

MR is often used to further evaluate unexplained nontraumatic (“spontaneous”) parenchymal bleeds. Hematoma signal intensity on standard sequences varies with clot age and imaging sequence. T2* (GRE, SWI) scans are especially important in evaluating patients with brain hemorrhage. SWI is particularly useful in identifying the presence and location of cerebral microbleeds.

Differential Diagnosis

The differential diagnosis of sICH varies widely with both anatomic location and patient age.

If a classic striatocapsular or thalamic hematoma is found in a middle-aged or older adult patient, hypertensive hemorrhage is, by far, the most common etiology (4-1) (4-4). Drug abuse should be suspected in a young adult with a similar-appearing lesion. Ruptured aneurysms rarely cause lateral basal ganglionic hemorrhage, and neoplasms with hemorrhagic necrosis are far less common than hypertensive bleeds in this location.

Lobar hemorrhages present a different challenge, as the differential diagnosis is much broader. In older patients, amyloid angiopathy, hypertension, and underlying neoplasm (primary or metastatic) are the most common causes (4-2) (4-5). Vascular malformations, especially AVMs (4-3) (4-6), are more common in children or young adults. Chronic vascular diseases, especially moyamoya angiopathy and sickle cell disease-associated angiopathy, are rare but important causes of ICH in children, while neoplasm-associated hemorrhage is rare.

Dural sinus &/or cortical vein thrombosis are uncommon but occur in patients of all ages and should not be overlooked.

Hemorrhages at the gray matter-white matter interface are typical of metastases (4-2), septic emboli, and fungal infection.

Multifocal hemorrhages confined to the white matter are rare (4-10). “Critical illness-associated” brain microbleeds occur in intubated patients with acute respiratory distress syndrome (ARDS), especially those who are on extracorporeal membrane oxygenation (ECMO). These may be hypoxia related, similar to the microbleeds seen in high-altitude cerebral edema.

When microbleeds are identified in a patient with SARS-CoV-2 or a history of a febrile illness followed by sudden neurologic deterioration, they are most likely secondary to a hemorrhagic form of acute disseminated encephalomyelitis called acute hemorrhagic leukoencephalopathy (AHLE, a.k.a. Weston-Hurst disease).

Clot age can likewise be helpful in suggesting the etiology of an ICH. A hemosiderin-laden encephalomalacic cavity in the basal ganglia or thalamus of an older patient is typically due to an old hypertensive hemorrhage. Cortical/subcortical microbleeds can be seen in cerebral amyloid angiopathy, particularly if siderosis is present.

Spontaneous (i.e., nontraumatic) primary intraventricular hemorrhage is rare. The most common causes are hypertension and occult vascular malformation in/around the ventricular wall.

“UNEXPLAINED” (NONTRAUMATIC) PARENCHYMAL BRAIN BLEEDS

Key Clinical Information

• Patient age, sex

• History (i.e., hypertension)

• Medications

Initial Imaging Survey

• NECT ± CTA

• Consider MR ± contrast if ≤ 55 years old

Key Imaging Features for Report

• Size

• Location

• Hematoma density (uniform vs. heterogeneous)