Abnormalities of Arterial Shape/Configuration

Anne G. Osborn, MD, FACR

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Effect of patient age on diagnosis
- Middle-aged or elderly
  - Atherosclerosis (ASVD)
  - Dolichoectasia
  - Saccular aneurysm
  - Fusiform aneurysm
- Child or young adult
  - Consider inherited vasculopathy (e.g., collagen-vascular disease like Ehlers-Danlos)
  - Child with fusiform vasculopathy: Check HIV status
  - Moyamoya
Is there evidence for hemorrhage?
- Subarachnoid
  - Saccular aneurysm ± vasospasm
  - Blood blister-like aneurysm
  - Dissection or dissecting aneurysm (especially vertebrobasilar)
- Parenchymal
  - Moyamoya (adult)
  - Vasculitis (especially drug-related)
  - Pseudoaneurysm (especially with trauma history)
Does lesion involve short or long segment of vessel, bifurcation vs. nonbranching point?
- Short, bifurcation → saccular aneurysm, ASVD
- Short nonbranching → pseudoaneurysm, blood blister-like aneurysm
- Long, nonbranching → ASVD, dolichoectasia, fusiform aneurysm (ASVD, non-ASVD), vasculitis, vasospasm

Helpful Clues for Common Diagnoses

Atherosclerosis, Intracranial
- Distal basilar artery (BA), cavernous/supraclinoid internal carotid artery (ICA) > cortical branches
- Findings
  - Normal aging: Arterial Ca++, wall thickening
  - Most common: Focal stenosis, luminal irregularities
  - Less common: Elongation/ectasia
  - Uncommon: Thrombosis, occlusion
- Remember: Most common cause of “vasculitis” appearance is ASVD, not vasculitis!
Dolichoectasia
- Elongation, dilatation, tortuosity without focal aneurysmal dilatation
- BA > ICA > MCA
- Slow flow may cause signal inhomogeneity, phase artifact
MR Artifacts, Flow-Related
- Pulsation may cause spin dephasing, signal loss in adjacent CSF (especially around distal basilar artery)
- Phase artifact propagation may distort vessel contours, propagate across imaged slice
- Slow flow & fully relaxed spins in entry slice(s) → T1 shortening may mimic thrombus
Saccular Aneurysm
- Round or ovoid outpouching ± “tit” or lobulations
- Arises from major vessel bifurcation
- Variable neck (narrow, wide, broad-based)
- Aneurysmal SAH common
Fusiform Aneurysm, ASVD
- Long segment irregular fusiform/ovoid arterial dilatation
- Vertebral arteries, BA > ICA, MCA
- Hematoma with variable aged clot common
- Residual lumen enhances strongly
- Variant = “giant serpentine aneurysm”
  - Large, partially thrombosed mass
  - Clot of varying age
  - No definable neck

Helpful Clues for Less Common Diagnoses

Vasospasm
- Etiology
  - Most common: Ruptured aneurysm → aSAH → vasospasm 5-7 days later
  - Less common: Trauma
- Imaging
  - Long- or short-segment stenosis
  - Often multifocal
  - ± Cerebral ischemia/infarction
Fusiform Aneurysm/Vasculopathy, Non-ASVD
- Fusiform or ovoid dilatation in absence of ASVD
- Long, affects nonbranching vessel segments
- Can be solitary or multifocal
- Vertebral/BA > carotid
- Younger patients
- Inherited (e.g., Ehlers-Danlos) or acquired (viral or collagen-vascular)
Dissection
- Can be traumatic or spontaneous
- May cause SAH
- Vertebral > > internal carotid artery
- Look for T1 hyperintense clot around residual lumen
- Focal dilatation → dissecting aneurysm
Pseudoaneurysm
- Cavitated clot lacks normal arterial wall
- Trauma, infection = common causes
- Peripheral location (distal to circle of Willis)
- Often adjacent to skull base or dura (tentorial incisura, falx)

Helpful Clues for Rare Diagnoses