Neuroradiology (1994) 36:614-615

Neuro--

radiology
9 Springer-Verlag 1994

Oculomotor nerve palsy due to thrombosis of a posterior
communicating artery aneurysm following diagnostic angiography
P. D. Griffiths 1, A. Gholkar 1, R. P. Sengupta 2
1 Department of Neuroradiology, Newcastle General Hospital, Newcastle upon Tyne, UK
2 Department of Neurosurgery, Newcastle General Hospital, Newcastle upon Tyne, UK
Received: 12 July 1993/Accepted: 2 September 1993

Abstract. W e p r e s e n t a p a t i e n t w h o d e v e l o p e d a painful
third n e r v e galsy two days after a n g i o g r a p h y h a d d e m o n s t r a t e d a large a n e u r y s m o n the P1 s e g m e n t of the left
p o s t e r i o r c e r e b r a l artery. C T at this stage d e m o n s t r a t e d
extensive t h r o m b u s within the previously u n c o m p l i c a t e d
a n e u r y s m . T h e h a e m o d y n a m i c s of this a n e u r y s m resulted in i n c o m p l e t e clearance of c o n t r a s t m e d i u m f r o m
its fundus and we posit that this m a y h a v e p r o m o t e d
t h r o m b u s f o r m a t i o n . Six m o n t h s later the a n e u r y s m was
s h o w n a n g i o g r a p h i c a l l y to be c o m p l e t e l y occluded.

Key words: O c u l o m o t o r n e r v e palsy - A n e u r y s m Thrombus formation - Contrast media
S p o n t a n e o u s occlusion of intracranial a n e u r y s m s is relatively u n c o m m o n . W e r e p o r t a case in which t h r o m b o s i s
of a large a n e u r y s m , a p p a r e n t l y as the result of angiography, gave rise to acute n e u r o l o g i c a l problems.

Case report
A 56-year-old man presented with a one year history of headache,
particularly in the left supraorbital region. He had no neurological
deficit and no relevant previous medical history. CT demonstrated
a homogeneously enhancing 2 x 2 cm aneurysm in the region of the
tip of the basilar artery (Fig. 1). At angiography this was shown to
be an aneurysm of the P1 segment of the left posterior cerebral artery. The aneurysm had a very narrow neck and contrast medium
cleared slowly from the sac (Fig. 2). As this was an unruptured aneurysm, the patient was listed for a routine embolisation procedure. Two days after the angiogram the patient complained of
worse headaches and was shown to have a complete left third nerve
palsy, contralateral hemiparesis and a fluctuating level of consciousness. CT showed abundant thrombus within the aneurysm
and there was minimal enhancement at its neck. The volume of the
aneurysm had increased (Fig. 3): by measuring from the hard copy
it was found that the aneurysm had changed from an approximate
Correspondence to: E D. Griffiths, Department of Neuroradiology,
Newcastle General Hospital, Westgate Road, Newcastle upon
Tyne, NE4 6BE, UK

volume of 5 c m 3 before angiography to 11 c m 3 2 days after the examination.
Seven months after the angiogram the patient presented again.
The right hemiparesis had resolved but there was a residual third
nerve palsy. New symptoms consisted of marked unsteadiness of
gait and intermittent zigzag lines throughout his visual fields. CT
and cerebral angiography (Fig.4) were performed. The former
demonstrated a nonenhancing, thrombosed aneurysm that had returned to its original preangiographic size. The chiasmatic cistern
was clearly visualised on this examination, while CT at the acute
thrombus stage had demonstrated complete obliteration of the cistern. No contrast medium entered the aneurysm at angiography,
indicating complete thrombosis, but there was also occlusion of the
proximal portion of the left P1 segment and distortion of the tip of
the basilar artery.

Discussion
T h r o m b u s f o r m a t i o n is a well r e c o g n i s e d p a r t of the natural history of s o m e aneurysms. I n partly t h r o m b o s e d
a n e u r y s m s the size of the l u m e n d e m o n s t r a t e d b y angiog r a p h y is significantly smaller t h a n the mass d e m o n strated on sectional imaging. T h r o m b o g e n e s i s p r o b a b l y
occurs o v e r a long time, and m a y p r o d u c e c o n c e n t r i c
layers of t h r o m b u s of different age, as s h o w n by M R I [1].
I a t r o g e n i c t h r o m b u s f o r m a t i o n in an a n e u r y s m , is usually
p r o d u c e d e n d o v a s c u l a r p l a c e m e n t o f materials such as
p l a t i n u m coils, has b e e n used as a m e t h o d o f treatment.
This case is u n u s u a l for two a n a t o m i c a l reasons. Firstly, the n a r r o w n e c k of the a n e u r y s m r e t a i n e d contrast
m e d i u m in the sac during angiography. Secondly, the
d o c u m e n t e d rapid increase in size directly after angiog r a p h y is unusual. E n l a r g e m e n t m a y o c c u r as p a r t o f the
n a t u r a l history of s o m e a n e u r y s m s but this p a t i e n t h a d
stable s y m p t o m s for o n e y e a r and s h o w e d e v i d e n c e of
severe mass effect only after angiography. It is t h e r e f o r e
likely t h a t the e n l a r g e m e n t o c c u r e d b e c a u s e of t h r o m b u s
f o r m a t i o n as a result of angiography.
T h e relationship b e t w e e n c o n t r a s t m e d i a and clotting
m e c h a n i s m s has b e e n the subject of m u c h research, b u t is
still p o o r l y u n d e r s t o o d . T h e u n d e r l y i n g principles a p p e a r
to be that w h e n b l o o d and saline a r e m i x e d in syringes,

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Fig.1. Contrast-enhanced CTat presentation. There is a uniformly
enhancing aneurysm adjacent to the left side of the midbrain. Note
the visibility of the chiasmatic cistern
Fig.2. Venous phase of left vertebral angiogram shows contrast
medium persisting in a large aneurysm on the P1 segment of the left
posterior cerebral artery
Fig. 3. Contrast-enhanced CT two days after the angiogram. There
is high attenuation thrombus within the fundus of the aneurysm and
a small amount of enhancement at its neck. The aneurysm has increased in volume; note the effacement of the chiasmatic cistern
Fig.4. Vertebral angiography demonstrates occlusion of the left P1
segment and non opacification of the aneurysm

contrast m e d i u m has anticoagulant properties. Nonionic
agents have less anticoagulant effects than ionic m e d i a
[2] and m a n y actually produce thrombosis in vitro [3].
Casalini's small study [4] d e m o n s t r a t e d clot in 60 % of
catheters used for angiography with nonionic m e d i a and
none within catheters used with ionic media. However,
there has b e e n no d o c u m e n t e d demonstration of any increase in t h r o m b o e m b o l i c events with nonionic m e d i a
[5]. The situation is different if contrast m e d i u m remains
in contact with tissues, as in this case. All contrast m e d i a
cause red cell and endothelial d a m a g e given sufficient
time and concentration [6]. The release of tissue-based
t h r o m b o g e n e t i c substances could be responsible for the
rapid f o r m a t i o n of t h r o m b u s in an aneurysm. We believe
that the thrombus within the a n e u r y s m was caused by the
contrast m e d i u m remaining in the sac. It is well recognised that acute t h r o m b i in other sites m a y be larger
than their p a r e n t vessel (c. f. the ultrasound appearances

of iliofemoral vein thrombosis). We suggest that a comparable event was responsible for the doubling in volume
of the aneurysm and d e v e l o p m e n t of s y m p t o m s in this
case.
We showed that the aneurysm returned to its preangiographic dimensions during the subsequent seven
months. This was p r e s u m a b l y due to clot retraction and
organisation. We accept that simple volume measurements f r o m CT images are inaccurate, particularly in the
craniocaudal plane. H o w e v e r , the significant changes in
volume of the t h r o m b o s e d a n e u r y s m during its evolution
can be inferred f r o m the effacement and subsequent reconstitution of the chiasmatic cistern.
Acknowledgements. The authors wish to thank Diane Dodds for her
help with the preparation of the manuscript and Audrey Kellett for
her photographic assistance.

References
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