Vascular Anomalies

Slide 1 · Vascular Anomalies

Structural anomalies • hemodynamic consequences • clinicopathologic recognition

Cerebral aneurysms | Arteriovenous fistulas | Fibromuscular dysplasia | Anomalous coronary origin

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Recognize how vascular wall architecture relates to blood flow and structural failure.

Explain the morphogenesis and major consequences of each of the four anomalies.

Differentiate aneurysm, direct arteriovenous shunt, stenosing dysplasia, and anomalous vessel course.

Apply the mechanisms to focused clinical and anatomic cases.

Recognize wall and flow

Explain four anomaly mechanisms

Predict anatomic complications

Apply clinicopathologic clues

Slide 3 · An anomaly can be clinically silent yet consequential

Many variations of the normal vascular supply produce no symptoms.

Unrecognized anatomy can complicate surgery or an endovascular procedure.

Clinical risk depends on vessel wall integrity, flow routing, and adjacent structures.

Saccular aneurysm

Outpouching

AV fistula

Direct shunt

Fibromuscular dysplasia

Stenosis / wall thinning

Coronary anomaly

Abnormal origin / course

Slide 4 · The four lesions disrupt different features

Berry aneurysm: Focal cerebral arterial wall outpouching.

Arteriovenous fistula: Direct artery–vein communication bypassing capillaries.

Fibromuscular dysplasia: Abnormal arterial wall thickening and stenosis, sometimes with aneurysm formation.

Anomalous coronary origin: A vessel originates or travels along an abnormal route.

Saccular aneurysm

Outpouching

AV fistula

Direct shunt

Fibromuscular dysplasia

Stenosis / wall thinning

Coronary anomaly

Abnormal origin / course

Slide 5 · Why the same variant may cause different outcomes

Site determines whether hemorrhage threatens brain, kidney or myocardium.

Structural weakness favors dilatation or rupture; Luminal loss favors ischemia.

Large shunts impose volume load; Vulnerable coronary courses may limit perfusion during exertion.

Altered wall / connection / course

Flow or mechanical consequence

Bleeding / ischemia / cardiac load

Slide 6 · Large-vessel walls have three basic layers

Intima: Endothelial lining that interfaces directly with flowing blood.

Media: Smooth muscle and elastic components adapted to local forces.

Adventitia: Supportive extracellular matrix and connective tissue.

Capillaries lack a conventional muscular media.

Lumen

Adventitia

Media

Intima

Slide 7 · Arteries and veins face different demands

Arteries sustain higher pressures and have relatively developed media.

Veins have more capacious lumens and thinner, less organized walls.

Capillaries trade structural complexity for efficient exchange.

Lumen

Adventitia

Media

Intima

Arterial wall

Vein

Slide 8 · A normal microvascular circuit prevents direct shunting

Arterial inflow supplies arterioles and a capillary exchange bed.

Flow then reaches postcapillary venules and larger veins.

A direct artery-to-vein connection bypasses the exchange bed and alters hemodynamics.

Artery

Vein

Arterioles

Capillary bed

Slide 9 · The site of a lesion matters as much as its size

A cerebral arterial branch point may form a weak-wall outpouching.

A renal artery lesion can reduce perfusion even without rupture.

An interarterial coronary course can become hazardous during exercise.

Saccular aneurysm

Outpouching

AV fistula

Direct shunt

Fibromuscular dysplasia

Stenosis / wall thinning

Coronary anomaly

Abnormal origin / course

Slide 10 · Wall structure explains two divergent complications

Weakness or attenuated media predisposes to aneurysmal dilatation.

Focal intimal or medial hyperplasia plus fibrosis may narrow the lumen.

The same disorder can have thickened segments adjacent to thinned, vulnerable ones.

Wall attenuation → aneurysm

Fibrosis / hyperplasia → stenosis

Fistulous connection → shunting

Slide 11 · A functional framework for classifying anomalies

Assess whether the abnormality is an outpouching, a shunt, a narrowed segment, or a displaced course.

Identify the affected vascular territory and the direction of flow.

Predict bleeding, ischemia, hypertension, or cardiac loading from anatomy rather than the label alone.

Saccular aneurysm

Outpouching

AV fistula

Direct shunt

Fibromuscular dysplasia

Stenosis / wall thinning

Coronary anomaly

Abnormal origin / course

Slide 12 · Saccular (“berry”) aneurysm: Core definition

A thin-walled saccular outpouching develops near cerebral arterial bifurcations.

Saccular aneurysms are the most common type of intracranial aneurysm.

Their principal catastrophic consequence is rupture with hemorrhage.

Saccular outpouching

Slide 13 · Why cerebral branch points are vulnerable

Bifurcations concentrate complex hemodynamic stresses on the vessel wall.

The affected wall lacks normal smooth muscle and internal elastic lamina in the sac region.

Underlying media defects and acquired flow stress contribute to aneurysm development.

Saccular outpouching

Slide 14 · “Congenital” does not mean present at birth

An underlying structural predisposition rather than a visible sac at birth.

Aneurysms develop over time at susceptible arterial sites.

Genetic and hemodynamic factors help explain why only some sites evolve into lesions.

Predisposed vessel architecture

Hemodynamic stress over time

Visible saccular aneurysm

Slide 15 · The critical wall defect is loss of reinforcement

Normal cerebral artery depends on an intact media and internal elastic lamina.

The sac lacks these structural components and is sustained by attenuated, fibrotic tissue.

Blood pressure acts on a wall with diminished mechanical support.

Parent artery: Reinforced wall

Sac: Attenuated fibrous wall

Slide 16 · Saccular aneurysms favor the circle of Willis

Approximately 90% of saccular aneurysms occur around branch points in the anterior circulation.

They lie along the circle of Willis or major proximal cerebral arteries.

Anatomic localization helps explain the pattern of basal subarachnoid hemorrhage.

Saccular outpouching

Slide 17 · Saccular aneurysms can be multiple

Multiple aneurysms in roughly 20–30% of cases.

Finding one aneurysm does not establish that no others exist.

Multiplicity matters when interpreting neurovascular anatomy and hemorrhage sources.

Saccular outpouching

Slide 18 · Susceptibility is usually multifactorial

Most saccular aneurysms occur sporadically.

Risk is increased among first-degree relatives of affected individuals.

Certain heritable connective-tissue and vascular disorders are associated.

Inherited predisposition

Structural arterial vulnerability

Hemodynamic and acquired exposures

Slide 19 · Examples of associated disorders

Autosomal dominant polycystic kidney disease is a recognized association.

Other reported associations include vascular Ehlers–Danlos syndrome, neurofibromatosis type 1, Marfan syndrome and aortic coarctation.

Fibromuscular dysplasia of extracranial arteries also occurs in association.

Slide 20 · Smoking and hypertension add acquired stress

Both smoking and hypertension are described as predisposing factors.

Hemodynamic stress may induce endothelial dysfunction at branch points.

An underlying vulnerable wall can enlarge progressively rather than remaining static.

Smoking and hypertension

Endothelial / wall stress

Saccular aneurysm susceptibility

Slide 21 · Unruptured aneurysm: The anatomic lesion

The lesion is an outpouching rather than a diffuse longitudinal narrowing.

The sac has a thin fibrotic wall and communicates with the parent artery.

An intact aneurysm may be detected before any hemorrhage occurs.

Saccular outpouching

Slide 22 · Histologic logic of a saccular aneurysm

At the sac, normal arterial wall layering is no longer preserved.

Loss of smooth muscle and elastic support contrasts with the adjacent parent artery.

A hyalinized fibrous aneurysm wall can be recognized histologically.

Parent artery: Reinforced wall

Sac: Attenuated fibrous wall

Slide 23 · Rupture leads most characteristically to SAH

Rupture of a cerebral saccular aneurysm is the most common cause of spontaneous subarachnoid hemorrhage.

Blood escapes into the subarachnoid compartment surrounding the brain.

The event can be immediately life-threatening.

Saccular outpouching

Slide 24 · Subarachnoid and parenchymal bleeding differ

Subarachnoid hemorrhage disperses blood into CSF-containing spaces.

Intraparenchymal hemorrhage directly damages adjacent brain tissue.

An intracranial hemorrhage pattern must be interpreted in its anatomic context.

Saccular outpouching

Slide 25 · Secondary complications extend beyond the rupture

Vasospasm after subarachnoid hemorrhage can compromise cerebral perfusion.

Healing can involve meningeal fibrosis and impaired CSF resorption.

These secondary responses help explain morbidity beyond the initial bleed.

Aneurysmal rupture

Subarachnoid hemorrhage

Vasospasm or meningeal scarring

Slide 26 · Berry aneurysm: Focused application

Illustrative case: Sudden severe headache with CT evidence of basal subarachnoid blood.

Which vascular defect is a leading spontaneous cause?

Predict the location and the principal wall abnormality before seeing angiography.

Slide 27 · Case interpretation: Aneurysmal SAH

A ruptured saccular aneurysm is the leading consideration within the supplied Robbins differential.

Look near cerebral arterial branch points, particularly in the anterior circulation.

The characteristic defect involves loss of normal medial smooth muscle and elastic lamina.

Slide 28 · Arteriovenous fistula: Defining topology

An arteriovenous fistula directly connects an artery to a vein.

The communication bypasses intervening capillary exchange channels.

A fistula is defined by flow routing—not by a tumor-like mass.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 29 · A shunt changes the normal circulatory pathway

A normal circuit passes through arterioles, capillaries and venules.

A fistula diverts some arterial blood directly to the venous system.

The magnitude of the shunt helps determine systemic consequences.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 30 · Fistulas may be congenital or acquired

Some are developmental defects.

Others arise when an arterial aneurysm ruptures into a nearby vein.

Penetrating injury or destructive inflammation can also connect adjacent vessels.

Developmental connection

Penetrating injury / inflammation

Aneurysm rupture into a vein

Slide 31 · Penetrating trauma can create a fistula

A wound crossing an artery and neighboring vein may establish a persistent channel.

Arterial pressure then drives blood into the lower-pressure venous circulation.

The mechanism is an acquired connection, not an intrinsic vascular neoplasm.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 32 · An aneurysm can rupture into an adjacent vein

A weakening arterial wall may communicate directly with a nearby venous lumen.

Such a connection combines a wall defect with pathologic shunting.

The consequence differs from an aneurysm rupturing freely into tissue.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 33 · Inflammation or necrosis can erode adjacent walls

Destruction of closely apposed arterial and venous tissue may breach both lumens.

The resulting channel creates a direct path for flow.

The etiologic route differs from a congenital anatomic connection.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 34 · Large fistulas can overload the heart

Substantial arterial-to-venous shunting increases venous return.

Sustained high-flow shunts increase cardiac workload.

A sufficiently large shunt can produce high-output cardiac failure.

Large artery-to-vein shunt

Increased venous return

Sustained cardiac workload

Possible high-output heart failure

Slide 35 · Rupture is another fistula complication

Fistulas, like aneurysms, can rupture.

The hemorrhagic risk is distinct from the hemodynamic burden of a persistent shunt.

Complications depend on location, vessel integrity and shunt magnitude.

Saccular aneurysm

Outpouching

AV fistula

Direct shunt

Fibromuscular dysplasia

Stenosis / wall thinning

Coronary anomaly

Abnormal origin / course

Slide 36 · Not every fistula is pathologic

Surgeons deliberately create arteriovenous fistulas for hemodialysis access.

The therapeutic fistula uses a high-flow artery-to-vein circuit to provide repeated vascular access.

An identical structural idea can therefore be purposeful or harmful depending on context.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 37 · Arteriovenous fistula versus AV malformation

A simple fistula denotes a direct connection between artery and vein.

Cerebral arteriovenous malformations contain abnormal networks of interconnected vessels.

Both can shunt blood; However, their architecture and clinical evaluation differ.

Pattern

Architecture

AV fistula

Direct artery–vein channel

Cerebral AVM

Tangled, high-flow network

Cavernous lesion

Low-flow dilated channels

Slide 38 · Cerebral AVM: Relevant contrast

Cerebral AVMs as tangled, high-flow vascular channels with intervening gliotic tissue.

They may cause seizures or intracranial hemorrhage.

This contrasts with a single direct fistulous communication and with low-flow cavernous malformations.

Abnormal cerebral vessels

Prominent arteriovenous shunting

Seizure or hemorrhage presentation

Slide 39 · Large neonatal cerebral shunts: An extreme example

Major arteriovenous malformations in newborns can produce congestive cardiac failure.

A vein of Galen malformation may connect malformed arteries directly to veins.

The example illustrates the impact of high-flow shunting on the circulation.

Artery

Vein

Direct connection

Capillary bed bypassed

Slide 40 · Arteriovenous shunt: Focused application

Illustrative case: An acquired direct artery–vein connection after penetrating injury.

Blood bypasses a capillary bed; A large shunt progressively increases cardiac output.

What mechanism connects the local lesion to systemic cardiac dysfunction?

Slide 41 · Case interpretation: High-output state

Persistent shunting diverts arterial blood into veins, increasing venous return.

The heart compensates by increasing output and may ultimately fail under sustained loading.

Shunt magnitude is the critical physiologic variable.

Slide 42 · Fibromuscular dysplasia: Core lesion

Fibromuscular dysplasia (FMD) produces focal, irregular thickening of muscular arteries.

The lesion involves hyperplasia and fibrosis, frequently in the media or intima.

Its major consequences are arterial stenosis and local wall weakness.

Alternating stenosis and dilatation

Slide 43 · FMD affects several muscular arterial beds

Renal, carotid, splanchnic and vertebral arteries.

The same wall disorder therefore has potential renal, cervical and visceral consequences.

The affected vessel determines whether ischemia, hypertension or an aneurysm is clinically prominent.

Vessel

Potential effect

Renal

Renovascular hypertension

Carotid / vertebral

Cervical arterial involvement

Splanchnic

Visceral arterial involvement

Slide 44 · The cause of fibromuscular dysplasia is unknown

Robbins does not establish a single causal genetic or environmental mechanism.

The morphologic substrate is uneven growth and fibrosis of the vascular wall.

A named arterial dysplasia should not be presumed inflammatory or atherosclerotic.

Cause not established

Irregular wall growth / fibrosis

Stenosis and adjacent attenuation

Slide 45 · Thickened arterial segments narrow the lumen

Focal intimal and medial hyperplasia increases wall thickness.

Fibrosis further reduces effective luminal caliber.

The resulting stenosis can reduce downstream organ perfusion.

Alternating stenosis and dilatation

Slide 46 · Thin segments can alternate with stenotic areas

Some arterial segments have markedly attenuated media.

These portions alternate with thickened, stenosing regions.

The resulting morphology explains the characteristic segmental angiographic pattern.

Alternating stenosis and dilatation

Slide 47 · “String of beads” is a structural descriptor

Angiography can show successive narrowings and relative expansions.

The beaded contour follows alternating focal stenosis and more dilated or attenuated segments.

It is not synonymous with inflammation or lipid-rich atherosclerotic plaque.

Alternating stenosis and dilatation

Slide 48 · Wall thinning adds risk beyond stenosis

Attenuated medial areas are less mechanically supported.

Aneurysms may arise in these weakened segments.

An aneurysm can rupture; FMD is therefore not solely a narrowing disorder.

Alternating stenosis and dilatation

Slide 49 · Renal FMD can initiate renovascular hypertension

Narrowing of a renal artery reduces the pressure and flow reaching the kidney.

The ischemic kidney increases renin production.

Renin–angiotensin signaling promotes systemic hypertension.

Renal artery stenosis

Reduced renal perfusion

Increased renin release

Angiotensin II / hypertension

Slide 50 · Renin links renal ischemia to vascular tone

Juxtaglomerular renin release activates the renin–angiotensin system.

Angiotensin II contributes to vasoconstriction and elevated systemic blood pressure.

Sodium retention can contribute to sustained renovascular hypertension.

Renal artery stenosis

Reduced renal perfusion

Increased renin release

Angiotensin II / hypertension

Slide 51 · Chronic renal artery stenosis changes the kidney

The ischemic kidney may shrink and develop diffuse atrophy.

Histology can include crowded glomeruli, tubular atrophy and interstitial fibrosis.

The contralateral kidney experiences the effects of increased systemic pressure.

Renal artery stenosis

Reduced renal perfusion

Increased renin release

Angiotensin II / hypertension

Slide 52 · Renal FMD differs from atherosclerotic stenosis

Atherosclerosis commonly narrows the renal arterial origin.

FMD is a heterogeneous dysplastic arterial thickening, often in younger patients.

FMD as more common in females than males.

Feature

Atherosclerosis | FMD

Mechanism

Intimal plaque | dysplasia

Renal pattern

Ostial plaque | segmental lesion

Context

Often older | often younger

Slide 53 · Fibromuscular disease has heterogeneous wall patterns

Renal FMD may involve intima, media or adventitia.

Do not infer a single histologic subtype from the diagnosis alone.

A medial-type lesion can show marked fibrous thickening and luminal narrowing.

Alternating stenosis and dilatation

Slide 54 · Interpreting a renal artery “beading” vignette

Illustrative case: A young adult with hypertension and multiple segmental renal arterial narrowings separated by expansions.

Identify the abnormal arterial wall process.

Explain the hypertension and a second structural complication beyond stenosis.

Slide 55 · Case interpretation: FMD of a renal artery

An irregular beaded muscular artery supports fibromuscular dysplasia.

Reduced renal perfusion stimulates renin release and the angiotensin system.

Medial attenuation can predispose to aneurysm formation and rupture.

Slide 56 · Normal coronary origin is paired and separated

Ordinarily, the left and right coronary arteries arise from their respective aortic sinuses.

Their proximal courses distribute oxygenated blood to the myocardium.

Origin and trajectory are both essential parts of coronary anatomy.

Aorta

Pulmonary artery

Separate proximal origins

Slide 57 · Anomalous coronary origin changes the ostium

Both coronary arteries originating above the same aortic valve cusp.

This is a developmental variant of coronary anatomy.

An abnormal origin alone does not determine clinical danger; Course is pivotal.

Aorta

Pulmonary artery

Course through the space between vessels

Slide 58 · An interarterial course defines an important hazard

An anomalous artery may pass between the aorta and pulmonary artery.

That position exposes the vessel to potential external compression.

The anatomic relationship becomes especially important during exertion.

Aorta

Pulmonary artery

Course through the space between vessels

Slide 59 · Exercise may compromise an interarterial vessel

Expansion and dynamic forces during exertion may compress a vulnerable coronary segment.

Restricted coronary flow can cause myocardial ischemia.

In the high-risk configuration, sudden death can occur.

Aorta

Pulmonary artery

Course through the space between vessels

Slide 60 · Most anomalous origins are not equally dangerous

Anomalous coronary origin is often benign.

The concerning scenario is an anomalous vessel passing between the great arteries.

Risk assessment requires understanding the actual proximal vessel course.

Aorta

Pulmonary artery

Course through the space between vessels

Slide 61 · Compression differs mechanistically from fixed plaque

Anomalous interarterial coronary artery: Course-dependent mechanical compromise.

Atherosclerotic coronary disease: Luminal narrowing from an intimal plaque.

Both can restrict myocardial blood supply, but the initiating pathology differs.

Mechanism

What limits flow?

Coronary anomaly

Course-related compression

Atherosclerosis

Plaque-related fixed stenosis

Slide 62 · Coronary origin: Focused application

Illustrative case: Collapse during exertion in a young person; An anomalous coronary artery arises above the same cusp as the other.

Its proximal segment runs between the ascending aorta and pulmonary trunk.

Identify the dangerous relationship and explain the potential loss of coronary flow.

Slide 63 · Case interpretation: Course-dependent ischemia

The interarterial coronary segment may be compressed by adjacent great vessels during exertion.

Impaired myocardial perfusion can provoke life-threatening ischemia.

The decisive feature is the artery’s trajectory, not merely an atypical ostium.

Slide 64 · Four anomalies: Morphology predicts consequence

Saccular aneurysm: Weakened bulging arterial wall → hemorrhage risk.

Arteriovenous fistula: Direct arterial–venous communication → high-flow shunt.

FMD: Alternating thickening and attenuation → stenosis ± aneurysm.

Anomalous coronary course: Great-vessel proximity → possible dynamic flow restriction.

Saccular aneurysm

Outpouching

AV fistula

Direct shunt

Fibromuscular dysplasia

Stenosis / wall thinning

Coronary anomaly

Abnormal origin / course

Slide 65 · Three distinct causes of reduced tissue perfusion

Arterial narrowing in FMD reduces renal inflow and may stimulate hypertension.

An interarterial coronary may compromise myocardial inflow mechanically during exertion.

Post-aneurysmal subarachnoid vasospasm can secondarily reduce cerebral perfusion.

Renal FMD → stenosis

Coronary anomaly → compression

SAH → vasospasm

Slide 66 · Hemorrhage risk: Three different anatomical sources

Berry aneurysm can rupture into subarachnoid spaces.

Arteriovenous fistulas can rupture from the abnormal connection.

FMD-associated aneurysms develop in thinned arterial segments and may rupture.

Saccular cerebral aneurysm

Arteriovenous fistula rupture

FMD-associated aneurysm rupture

Slide 67 · Recognize the anomaly from the dominant clue

Branch-point cerebral outpouching points to a saccular aneurysm.

An artery directly entering a vein points to a fistula.

Segmental stenoses with beading suggest FMD; An interarterial coronary requires origin-and-course analysis.

Where is the vessel?

Is it narrow, dilated or connected?

Which organ is downstream?

What clinical consequence follows?

Slide 68 · Anomaly recognition in procedures

Identify unexpected branches and variant ostia before placing devices or operating.

A catheter or stent cannot be planned solely from an assumed normal vascular map.

Where a lesion is incidental, the relevant risk still depends on course, wall integrity and flow pattern.

Map origin and course

Assess lumen and connections

Anticipate procedural hazards

Slide 69 · Integrated teaching case: Four observations

A: Basal subarachnoid blood following sudden headache.

B: High cardiac output with a direct artery–vein communication.

C: Renin-associated hypertension with a beaded renal artery.

D: Exercise-associated ischemia and an interarterial coronary segment.

Slide 70 · Integrated case: Assign the underlying lesion

A: Ruptured saccular aneurysm at a cerebral branch point.

B: Large arteriovenous fistula causing high-flow shunting.

C: Renal fibromuscular dysplasia causing stenosis and ischemia.

D: Anomalous coronary origin with a high-risk interarterial course.

Slide 71 · Essential distinctions for clinical pathology

Structural dilatation, direct shunting, stenosing dysplasia and anomalous course are not interchangeable diagnoses.

Morphology should be tied to the mechanism of hemorrhage, ischemia, hypertension or cardiac loading.

Cross-sectional vascular anatomy guides interpretation even when an anomaly is asymptomatic.

Slide 72 · References and source boundaries

Primary: Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed. (2026), Chapter 11, pp. 441–444.

Additional passages from the same text: Chapter 28, pp. 1141–1143, cerebral aneurysms/vascular malformations.

Additional passages: Chapter 20, pp. 852–853, renovascular hypertension/FMD; Chapter 10, pp. 432–433, pediatric malformations.

Visuals are original editable schematics; no reproduced pathology images or proprietary textbook figures.