3D Angiographic Atlas of Neurovascular Anatomy and Pathology Practice Flashcards

Overview and Foreword by Dr. Robert F. Spetzler

  • Perspective on Diagnostic Imaging: Dr. Spetzler highlights the rapid evolution of neuroimaging, noting that a single generation has moved from lesions considered "occult" in one modality to those easily diagnosed with pathognomonic features in another.

  • Evolution of Cavernous Malformations: Historically, cerebral cavernous malformations were often misidentified as "angiographically occult arteriovenous malformations."

  • Neurosurgical Benefits of 3D Rotational Angiography (3DRA):     * Provides high accuracy in diagnosis and treatment optimization for challenging neurovascular disorders.     * Preoperative planning is significantly improved by the ability to rotate images to see posterior vessel regions.     * The "Dark Side of the Moon" Metaphor: Assessing the neck of an aneurysm to determine suitability for clipping or identifying vessels that must be spared is compared to viewing the dark side of the moon—unprecedented visual access compared to conventional 2D methods.     * Educationally, $3DRA$ helps trainees translate 2D textbook images into 3D spatial understanding.

  • Background of Neil M. Borden, MD: Described as a "walking radiology encyclopedia," Dr. Borden completed fellowships at the Neurological Institute of New York and the Barrow Neurological Institute.

Introduction to Three-Dimensional Rotational Angiography

  • Evolution of Modalities: The author transitioned from angiographic cut film to 2D digital subtraction angiography ($2D\,DSA$) and finally to 3D rotational angiography ($3DRA$).

  • Core Goal of Anatomical Imaging: Recreating the in vivo status as close to the natural state as possible.

  • The Three Key Advantages of 3D Display:     1. Accuracy: Improved representation of pre-existing anatomy over 2D limitations.     2. Prognosis and Intervention: Better decision-making for conservative management, traditional surgery, or endovascular intervention. Traditional 2D methods involve data loss during transformation from 3D objects.     3. Education: Provides the dimension of depth, which is critical for understanding the tortuous and inconstant cerebral vascular tree.

  • Clinical Utility in Aneurysms: $3DRA$ allows for precise assessment of:     * Aneurysm neck morphology.     * The takeoff of vascular branches.     * Relationships of vessels to the walls of the aneurysm.     * Unobtrusive views of the posterior wall of vessels, which are often invisible during surgery or in standard $DSA$.

  • Limitations of $3DRA$:     * Difficulty in demonstrating very small distal branches of the vascular tree.     * Lack of background bony landmarks for spatial reference.     * Lack of sequential visualization showing contrast progression phases (arterial to capillary to venous).     * $3DRA$ is a complement to, not a replacement for, high-resolution $2D\,DSA$.

Technique of Three-Dimensional (3D) Rotational Angiography

  • Conventional Catheter Angiography: Involves injecting positive contrast via a catheter inserted percutaneously, usually via the femoral artery in the groin (axillary or brachial arteries are alternatives).

  • The $3DRA$ Process:     * A movable X-ray tube rotates in an arc around the patient while contrast is injected.     * Data is sent to a computer workstation to generate a 3D model.

  • Equipment Specifics (General Electric Equipment):     * Scanner: GE LCN+ equipment with a Sun workstation.     * Rotation: The floor-mounted C-arm rotates approximately 220220 degrees.     * Speed: 4040 degrees per second.     * Duration: Acquisition takes approximately 55 seconds.     * Frame Rate: Approximately 8.88.8 frames per second, totaling 4444 images.     * Resolution: Matrix size of 512×512512 \times 512.

  • Preparation and Isocenter:     * The Region of Interest (ROI) must be in the isocenter in both frontal (AP) and lateral projections under fluoroscopy.     * Safety Check: A "test rotation" is mandatory to prevent collisions with anesthesia equipment, ventilators, or drainage catheters.

  • Injection Parameters:     * Objective: Maintain complete opacification for the full 55-second sequence.     * Typical Dose: Total volume of 15 cc15\,cc at a rate of 3 cc/sec3\,cc/sec.     * Modifications: Adjustments are made based on vessel size, cardiac output, or high-flow states like AVMs.     * Delay Times: Usually 0.50.5 to 22 seconds, depending on the distance from the catheter tip to the ROI and the patient's cardiac output.

  • Reconstruction Algorithms:     * Shaded Surface Display (SSD): Simulates a light source to generate shades of gray for 3D perspective.     * Maximum Intensity Projection (MIP): Focuses on the highest intensity pixels.     * Volume Rendering (VR): A comprehensive 3D modeling technique.     * Navigator View: Provides an endoluminal view (simulating a camera inside the vessel).

The Aortic Arch

  • Anatomy:     * The arch carries blood from the left ventricle through the ascending thoracic aorta (length of 44 to 5 cm5\,cm).     * The diameter of the arch beyond the great vessels is approximately two-thirds that of the ascending aorta.

  • Great Vessels (Standard Order):     1. Innominate Artery: Divides into the right common carotid and right subclavian arteries.     2. Left Common Carotid Artery (LCCA): Arises from the arch in 75%75\% of cases; may share a common origin with the innominate artery.     3. Left Subclavian Artery (LSCA): The most left-sided branch.

  • Vertebral Artery Origins:     * Normal: Right and Left vertebral arteries usually arise from their respective subclavian arteries.     * Anomaly: The Left vertebral artery arises directly from the arch in 6%6\% of cases, usually entering the spine at C4 or C5.     * Standard entry to the foramen transversarium: 95%95\% enter at C6.

  • Arch $3DRA$ Challenges: Large contrast volumes are required, and motion artifact from cardiac/aortic pulsation often degrades image quality.

Cervical Vasculature

  • Carotid Circulation:     * Common Carotid Artery (CCA): Bifurcates most commonly at C3-4 (34%34\%) or C4-5 (46%46\%).     * Internal Carotid Artery (ICA): Ascends vertically with no major named branches in the neck; enters the carotid canal in the petrous bone.     * External Carotid Artery (ECA): Tortuous course supplying the face, scalp, and dura.

  • Internal Maxillary Artery (IMAX) Segments:     1. First (Mandibular): Branches include middle meningeal, accessory meningeal, and inferior alveolar.     2. Second (Pterygoid): Branches include buccal, masseteric, and deep temporal muscular branches.     3. Third (Pterygopalatine): Branches include infraorbital, sphenopalatine, and the vidian artery.

  • Clinical Warning (Middle Meningeal Artery): A petrous branch can supply the facial nerve (CN VII). Embolizing with small particles can cause facial paralysis. Anastomosis with the ophthalmic artery can also lead to blindness or collateral flow during ICA occlusion.

  • Vertebral Arteries:     * Course: Enter C6 and ascend to C2, turn superolaterally, then curve around the atlanto-occipital joint to enter the foramen magnum.     * Asymmetry: The left vertebral artery is often larger than the right; hypoplasia is common.

Intracranial Carotid and Anterior Circulation

  • ICA Segments (Fischer Nomenclature):     * Petrous: Vertical and horizontal.     * Presellar: (Fischer C5).     * Intracavernous: Horizontal (Fischer C4) and Anterior Genu (Fischer C3).     * Supraclinoid: Proximal (C2) and Distal (C1).

  • Key Branches:     * Meningohypophyseal Trunk (MHA): Arises at the C5-C4 junction.     * Ophthalmic Artery: Usually arises intradurally just above the dural ring.     * Anterior Choroidal Artery: Frequently seen on $3DRA$.

  • Middle Cerebral Artery (MCA):     * Bifurcates in 75%75\% of cases; trifurcates in 25%25\%.     * Sylvian Point: The most superior/medial point where the last sylvian MCA branch turns inferolaterally.

  • Anterior Cerebral Artery (ACA):     * Recurrent Artery of Heubner: Arises from distal A1 or proximal A2; supplies the caudate head and internal capsule.

Posterior Circulation and Venous System

  • Intracranial Vertebral Branch: Posterior Inferior Cerebellar Artery (PICA). There is a reciprocal size relationship between PICA and the Anterior Inferior Cerebellar Artery (AICA).

  • Basilar Artery Branches: AICA, Pontine perforators, Superior Cerebellar Artery (SCA), and Posterior Cerebral Artery (PCA).

  • PCA Segments:     * P1 (Peduncular): From basilar tip to PCoA.     * P2 (Ambient): Within the crural/ambient cistern.     * P3 (Quadrigeminal): Approaches the splenium of the corpus callosum.

  • Fetal Origin PCA: In 20%20\% of people, the PCA arises directly from the ICA; the P1 segment is hypoplastic.

  • Venous Drainage:     * Dural Sinuses: Includes Superior Sagittal Sinus (SSS), Straight Sinus, and Cavernous Sinuses.     * Superficial Veins: Vein of Trolard (superior drainage) and Vein of Labbé (inferior temporal drainage).     * Deep Veins: Internal Cerebral Veins and Great Vein of Galen.

  • Developmental Venous Anomaly (DVA): Characterized by a "medusa head" of small vessels draining into a single large stem.

The Circle of Willis

  • Function: A polygonal collection of arteries providing collateral flow between anterior and posterior circulations.

  • Prevalence: A complete "classic" Circle of Willis is present in only 18%18\% of the population.

  • Common Variants:     * Hypoplasia or absence of A1 segment (25%25\%).     * Hypoplasia or absence of PCoA (32%32\%).     * Fetal origin of PCA (1515-22%22\%).

  • Diagnostic Maneuver: External neck compression of the contralateral carotid artery during injection can test the functional patency of the anterior and posterior communicating arteries.

Anterior Circulation

  • Overview: The anterior circulation plays a significant role in supplying blood to the anterior and superior parts of the brain. This primarily involves the internal carotid arteries (ICA), which branch off from the common carotid arteries and supply key regions of the cerebral hemispheres. The anterior circulation is crucial for cognitive functions, motor skills, and the overall metabolic needs of the brain.

  • Internal Carotid Artery (ICA) Segments (Fischer Nomenclature):

    1. Petrous Segment:

      • Description: This segment runs through the petrous portion of the temporal bone, transitioning into the horizontal segment as it approaches the cavernous sinus.

      • Significance: Supplies adjacent structures such as the middle and inner ear. Its anatomical relationship with neighboring cranial nerves is important for surgical approaches in this area.

    2. Presellar Segment:

      • Description: (Fischer C5) The segment just prior to entering the cavernous sinus.

      • Significance: Knowledge of this segment is critical during the management of sellar tumors, as it is adjacent to the pituitary gland and the cavernous sinus, where vascular complications can occur during tumor removal.

    3. Intracavernous Segment:

      • Description: Comprised of both the horizontal (Fischer C4) and anterior genu (Fischer C3) components as the ICA passes through the cavernous sinus.

      • Significance: This segment is vulnerable to pathology, such as carotid-cavernous fistulas, that can lead to devastating neurological implications, including cranial nerve palsies due to its proximity to cranial nerves III, IV, V (both V1 and V2), and VI.

    4. Supraclinoid Segment:

      • Description: Above the clinoid process, further divided into proximal (C2) and distal (C1) segments.

      • Significance: This area is crucial as it gives rise to significant branches like the anterior and middle cerebral arteries (ACA and MCA), which supply the majority of the cerebral cortex. Variations in this segment can impact vascular surgical interventions.

  • Key Branches of the Anterior Circulation:

    • Meningohypophyseal Trunk (MHA):

      • Origin: Arises at the C5-C4 junction.

      • Supply: Provides blood to the dura mater, sphenoid, and hypophysis (pituitary gland). Its anatomical variability must be appreciated during endonasal transsphenoidal approaches.

    • Ophthalmic Artery:

      • Origin: Emerges intradurally just above the dural ring as the first major branch of the ICA.

      • Supply: Supplies the eye and its blood vessels, including the central retinal artery. Occlusion of this artery can lead to vision loss; hence, its assessment is vital in cerebrovascular diseases.

    • Anterior Choroidal Artery:

      • Frequency: Commonly visible in imaging, this branch arises from the supraclinoid ICA.

      • Supply: This artery supplies critical areas including the phrenic nucleus, parts of the thalamus, and choroid plexus. Infarcts could induce sensory disturbances and hemianopsia, especially due to its role within the visual pathways.

  • Middle Cerebral Artery (MCA):

    • Branches: Divides into multiple branches in about 75% of individuals (bifurcates) and can trifurcate in around 25%.

    • Function: Supplies the lateral portions of the cerebral hemisphere, including the primary motor and sensory cortices for the upper limbs and face.

    • Sylvian Point:

      • Description: The critical point at which major branches of the MCA bifurcate and ascend to supply specific cortical areas.

      • Significance: A key anatomical marker for neurosurgery, as lesions or strokes in this territory can lead to expressive aphasia or contralateral motor deficits.

  • Anterior Cerebral Artery (ACA):

    • Branches:

      • Recurrent Artery of Heubner:

        • Origin: Arises from the A1 or proximal A2 segment.

        • Supply: Supplies the caudate nucleus and anterior limb of the internal capsule, involved in voluntary motor control pathways. Damage to this artery can lead to significant motor deficits, especially affecting the leg.

  • Clinical Relevance:

    • Anatomy and Variations: Understanding the details of anterior circulation anatomy and its variations becomes critical for diagnosing and managing cerebrovascular diseases. The presence of accessory vessels or anomalous branches must be accounted for during surgical planning and intervention.

    • Pathological Implications: Occlusions or stenosis within the anterior circulation can result in ischemic strokes leading to specific motor and sensory deficits that are geographically correlated with the affected arterial territory. Symptoms based on the affected area include weakness, sensory loss, or higher cortical deficits, such as aphasia if the dominant hemisphere is involved.

    • Imaging and Treatment Approaches: Utilizing imaging modalities such as MR angiography, DSA, and 3D Rotational Angiography (3DRA) allows for optimized visualization of vascular structures and anomalies guiding treatment decisions. Treatment primitive options include medical management, stenting, or surgical interventions like bypass grafting or aneurysm clipping, tailored based on specific vascular configurations and clinical presentations.