Can CTA or MRA replace intra-arterial digital subtraction angiography (DSA) in the investigation of isolated third nerve palsy?

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Can CTA or MRA replace intra-arterial digital
subtraction angiography (DSA) in the
investigation of isolated third nerve palsy?

• William A. Fletcher, M.D., FRCPC
• University of Calgary

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DSA?Or is MRA or CTA sufficient? Kissel et al
(1983)25 aneurysmal palsies 12 pupil-sparing
incomplete
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Third Nerve Palsy Can CTA or MRA Replace DSA?

• 3 Questions
• Sensitivity of CTA and MRA in detecting
  aneurysms?
• Prevalence of aneurysm in III palsy?
• With pupil-sparing incomplete palsy
• With relative pupil-sparing palsy
• Risk of complications from DSA?

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III Nerve Palsy MRA?

• Jacobson and Trobe (1999)
• Risk of MRA missing P Comm aneurysm
• 1.5

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Posterior Communicating Artery (P-Comm) Aneurysms
Causing Third Nerve Palsy

• Jacobson and Trobe (1999)

Aneurysm Diameter Proportion causing palsy () Not detected by MRA () Proportion causing palsy not detected by MRA ()
? 5 mm 91.3 x 3 2.7
? 5 mm 8.7 x 46 4.0
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P-Comm Aneurysms Causing Third Nerve Palsy

• Jacobson and Trobe (1999)

AneurysmDiameter Proportion causing palsy not detected by MRA () 8-Year Rupture Rate () Proportion not detected by MRA and liable to rupture ()
? 5 mm 2.7 x 31 0.85
? 5 mm 4.0 x 16 0.65
Total 1.5
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P-Comm Aneurysms

• International Study of Unruptured Intracranial
  Aneurysms (ISUIA) (2003)
• 5-year risk of rupture
• ? 7 mm 2.5
• 7 12 mm 14.5

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Symptomatic Unruptured Aneurysms Risk of Rupture

• Juvela et al (1993 2000)

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Symptomatic Unruptured Aneurysms

• Yanaka et al (2003)
• 16 patients with acute third nerve palsies
• all aneurysms ? 10 mm
• 1 aneurysm (6mm) ruptured on day 3
• ?risk of rupture unknown

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P-Comm Aneurysms Causing III Nerve Palsy

• Jacobson and Trobe (modified)

Aneurysm Diameter Proportion causing palsy () Not detected by MRA () Not detected by MRA () Proportion not detected by MRA and liable to rupture ()
? 5 mm 91.3 x 3 x 3 2.7
? 5 mm 8.7 x 46 x 46 4.0
Total 6.7 Total 6.7
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MRA Sensitivity for Detecting Aneurysms

• White et al (2000)
• ? 3 mm 94
• Kupersmith et al (2005)
• Prospective study of MRA

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MRA Sensitivity for Detecting Aneurysms

• Kupersmith et al (2005)

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MRA Sensitivity for Detecting Aneurysms

• White et al (2000)
• ? 3 mm 94
• Kupersmith et al (2005)
• Prospective study of MRA
• ? 3 mm 100 (n 42)
• Confidence interval 93 - 100

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P Comm Aneurysms Causing Third Nerve Palsy

• Jacobson and Trobe (modified again)

AneurysmDiameter Proportion causing palsy () Not detected by MRA () Not detected by MRA () Proportion not detected by MRA and liable to rupture ()
? 3 mm 100 0 - 7 0 - 7 0 - 7


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CTA Sensitivity for Detecting Aneurysms
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CTA Sensitivity for Detecting Aneurysms

• Hoh et al (2004)
• 225 aneurysms
• 109 ruptured
• 114 unruptured
• 28 P Comm aneurysms
• Sensitivity 100
• CI95 overall 98.7 - 100
• CI95 unruptured aneurysms 97.4 100

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CTA Sensitivity for Detecting Aneurysms

• Kangasniemi et al (2004)
• 168 aneurysms ? 2 mm
• Sensitivity 99.4 (CI 97 100)

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CTA Sensitivity for Detecting Aneurysms

• 8 studies of multi-slice CTA and aneurysms
• 712 aneurysms 3mm on DSA
• 1.1 not visible on CTA ( 98.9 sensitivity)
• 1.4 observer error ( 97.5 sensitivity)
• ? Lower CI95 CTA senstivity 96 - 97.8

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CTA Sensitivity for Detecting Aneurysms

• Multislice helical CT

Aneurysm Diameter Proportion causing palsy () Not detected by CTA () Proportion not detected by CTA and liable to rupture ()
? 3 mm 100 0 - 3 0 - 3
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Third Nerve Palsy Can CTA replace DSA?

• 3 Questions
• Sensitivity of CTA in detecting aneurysms?
• Prevalence (pre-CTA probability) of aneurysm in
  TNP?
• With pupil-sparing incomplete palsy
• Risk of complications from DSA?

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Pupil-sparing incomplete palsy Pre-CTA
probability of aneurysm
Cause Proportion of all 3rd nerve palsies () Proportion pupil-sparing incomplete () Proportion of all 3rd n palsies pupil-sparing incomplete ()
Aneurysm 18 x 13 (n64) 2.3
Ischemia 40 x 46 (n141) 18

• ? Maximum Pre-CTA probability 12 (2.3/20.3)

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Pupil-sparing incomplete palsyProbability of
aneurysm after normal CTA
Maximum Pre-CTA Probability () Minimum CTA Sensitivity () Maximum Post-CTA Probability ()
12 97 ? 0.4
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Third Nerve Palsy Can CTA replace DSA?

• 3 Questions
• Sensitivity of CTA in detecting aneurysms?
• Prevalence (pre-CTA probability) of aneurysm in
  TNP?
• With relative pupil-sparing palsy
• Risk of complications from DSA?

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Relative pupil-sparing palsy Pre-CTA probability
of aneurysm
Cause Proportion of all 3rd nerve palsies () Relative pupil-sparing () Proportion of all 3rd n palsies relative pupil-sparing ()
Aneurysm 18 x 12 2.2
Ischemia 40 x 14 5.6

• ? Maximum Pre-CTA probability 28 (2.2/7.8)

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Relative pupil-sparing palsy Probability of
aneurysm after normal CTA
MaximumPre-CTA Probability() Minimum CTA Sensitivity() Maximum Post-CTA Probability ()
28 97 ? 1.2
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Third Nerve Palsy Can CTA replace DSA?

• 3 Questions
• Sensitivity of CTA in detecting aneurysms?
• Prevalence (pre-CTA probability) of aneurysm in
  TNP?
• Risk of complications from DSA?

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Risk of complications from DSA?

• Permanent neurological complications
• Cloft et al (1999) meta-analysis
• 3,517 studies 0.3 (upper CI95 - 0.5)
• Willinsky et al (2003) prospective
• 2,899 studies 0.5 (upper CI95 - 0.7)

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Factors modifying CTA sensitivity

• CTA technology, quality, interpretation

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Factors modifying aneurysm prevalence

• Age lt 50-years old
• Chou et al (2004)
• 29 III nerve palsy patients 50-years old
• 86 ischemia, 7 aneurysm

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Factors modifying aneurysm prevalence

• Gender
• MF ratio - 13 for PComm aneurysms
• Capo et al (1992) Renowden et al (1993)
• 75 patients with III palsy women men
• aneurysm 24 7
• ischemia 50 59
• Max. post-CTA risk
• Pupil-sparing incomplete 0.4 0.1
• Relative pupil-sparing 1.2 0.3

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Pupil-Sparing Incomplete PalsyCaveats

• Pupils should be re-examined within a week of
  onset
• Isolated superior division palsy greater risk ?

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Relative Pupil-Sparing PalsiesCaveats

• Pupils should be re-examined within a week of
  onset
• Anisocoria 2.0 mm

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DSA after negative CTA?

Internal Dysfunction Internal Dysfunction Internal Dysfunction Internal Dysfunction
External Dysfunction None Partial Complete
External Dysfunction Partial No DSA, unless Agelt 50 OR Sup divn palsy DSA, unless Male 50-years old AND Anisocoria lt 2 mm AND External dysfunctn DSA
External Dysfunction Complete No DSA DSA, unless Male 50-years old DSA