What’s the reason for this lady’s first-time seizure?
Vol.20, No.05, August 2012

A 49-year-old woman presented to the ER with a first-time seizure. She’d been previously well with no significant contributory history. She suffered no lingering after-effects from the seizure. Her lab results were unremarkable. A CT scan of the head was performed without, then with, IV contrast (Figures 1 & 2).

What’s the most likely cause of this woman’s first-time seizure?

a) acute left parietal hemorrhagic stroke with peri-infarct enhancement

b) cerebral Ascaris lumbricoides (nematode roundworm) infection

c) glioblastoma multiforme cerebral neoplasm

d) sinus pericranii

e) cerebral arteriovenous malformation (AVM)

ANSWER
Solution to Analyze This!

e) cerebral arteriovenous malformation (AVM)

The mildly hyperdense vermiform structure in the lateral left parietal region in Figure 1 (arrows) in fact represents a large abnormally dilated draining vein, as a result of the presence of the more central arteriovenous malformation (AVM) identified after administration of IV contrast (smaller arrows, Fig. 2). An AVM is a serpiginous tangle of abnormal and poorly formed arteries and veins that can develop almost anywhere within the body. They have a higher rate of bleeding than normal vessels due to the weakened wall structure. The risk of hemorrhage is about 4% per year. Cerebral AVMs are of greater clinical importance due to the potentially catastrophic effects that can result if and when they bleed. They are, thankfully, rare, occurring in approximately 1% of the general population. AVMs are considered to be congenital and most are likely present at birth. A small percentage of AVMs may be genetic in origin, as with those accompanying patients with hereditary hemorrhagic telangiectasia (HHT). An AVM is not a tumour or neoplasm, and will never metastasize to other parts of the body. Rarely, AVMs may develop as a result of trauma, as seen with dural AVMs post-injury. AVMs have no racial or geographic predilection and occur in the sexes in almost equal proportions. The typical time of discovery is between ages 20 and 40 years. Non-hemorrhage related symptoms include headache and seizure. The annual potential mortality rate from cerebral AVMs is around 1%.

Once discovered, most cerebral AVMs can be successfully treated with non-surgical procedures, including a variety of imaging-guided endovascular embolization/occlusion techniques (utilizing glues and/or coils), with a team approach often involving neurologists, neurosurgeons and interventional neuroradiologists. If any flow persists through the lesion post-treatment, the risk of bleeding persists, so close follow-up and repeat therapies are often required. Pre-surgical embolization techniques can also improve post-surgical results. In some cases, focused stereotactic radiation (radiosurgery) is used to obliterate the abnormal vessels. The decision whether or not to treat a particular cerebral AVM depends on expected potential side effects from treatment options, weighted against the risk of the natural history of the untreated lesion.

The appearance and density of the tubular lesion identified in Fig. 1 is not in keeping with a focal intra-axial hemorrhage and as such the option of hemorrhagic stroke shouldn’t be considered. However, in patients who do suffer acute strokes, a pattern of peripheral enhancement can be seen on post-contrast studies surrounding the infarcted tissue (peri-infarct enhancement, known as luxury perfusion), the bodies attempt to increase local cerebral blood flow to preserve as much tissue as possible. Cerebral round worm infection is highly unlikely, despite the vermiform appearance of the dilated vein on Fig. 1. Humans are the definitive host for the nematode roundworm Ascaris lumbricoides, but the site of involvement of most is commonly the intestines. Cerebral A. lumbricoides is exceedingly rare but may result from larva migrans and is most likely to present as either encysted larva or a cerebral abscess, not a viable ascaris worm per se. Glioblastomas (malignant gliomas) are the most common adult malignant brain tumours, and 20% of all primary brain neoplasms are glioblastoma multiforme (GBM) tumours. GBM is the highest-grade form of astrocytoma and makes up about two-thirds of all brain astrocytomas. The prognosis for this tumour is very poor. GBMs can present with highly variable appearances, it may sometimes mimic other conditions such as an infarct, an abscess, or even a necrotic dominant plaque in multiple sclerosis and thereby delay diagnosis. Although GBM is a possible consideration in our case, the post contrast appearance is classic for AVM, not GBM. Sinus pericranii is an unusual venous anomaly characterized by communication of superficial epicranial varicosities with an underlying dural venous sinus. The varicosities are intimately associated with the periosteum, are distensible, and vary in size with changes in intracranial pressure. Symptoms are infrequent but include headache, vertigo, feelings of fullness, or local pain. Typically, imaging will reveal an abnormal venous connection through the calvarium. Although the dilated peripheral cerebral vein could cause one to consider this diagnosis, the more central serpiginous cluster of abnormal vessels seen post-contrast would seal the diagnosis of AVM instead.

References

  1. Lee EJ et al. AJR 2011;196:71-6.
  2. Carpenter JS et al. Am J Neuroradiol 2004;25:121-5.
  3. Weill A et al. Interventional Neuroradiol 2001;7:115-20.
  4. Hatazawa J et al. Stroke 1999;30:800-6.
  5. Ondra SL et al. J Neurosurg 1990;73;387-91.
  6. http://mitpress.mit.edu/e-journals/JCN/articles/002/Tatter.html
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Clinical challenge image
Figure 1: Select axial unenhanced CT of the head at the level of the lateral ventricles. The scan reveals a mildly hyperdense vermiform structure in the lateral left parietal region (arrows). There’s no associated edema or shift.
Clinical challenge image
Figure 2: Select axial CT image of the head at the same level of the lateral ventricles, following IV contrast. There’s homogeneous enhancement of the tubular structure (long arrows) along with a serpiginous focus centrally in the left corona radiata location (small arrows). Again, there’s no edema or mass effect. No other enhancing lesions were present elsewhere on the scan (not shown).
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