Symptomatic Perianeurysmal Edema Following Bare Platinum Embolization of a Small Unruptured Cerebral Aneurysm

Discussion

Adverse inflammatory reactions have been described following coil embolization of cerebral aneurysms and may manifest in a variety of clinical ways. These include headache, lethargy, meningism, blindness, confusion, and impaired cognition.^1–15 MR imaging has been performed in some instances and has variably demonstrated hydrocephalus, aneurysm enhancement, perianeurysmal edema, and perianeurysmal enhancement.^2,3,7,9–11 Observation of such events has coincided with the increasing use of modified “bioactive” coils, and a causal link has been suggested.

Perianeurysmal edema is not a new phenomenon and has been described with both treated and untreated cerebral aneurysms. The latter are usually large or partially thrombosed lesions, often embedded in the substance of the brain.⁷ Following coil embolization, certain patients have developed de novo edema, whereas treatment has also been associated with a reduction or resolution of the brain edema in others.¹² The mechanism by which edema develops around an aneurysm is unclear, and various interrelated factors have been postulated. These include intraluminal thrombosis, aneurysm pulsatility, intramural hemorrhage, wall inflammation, and cytokine release.^2,12 Some patients respond to steroid therapy, a feature that supports an inflammatory etiology, as does the observation of increased white cells and protein in the CSF of certain patients⁴; however, complete symptomatic improvement is not always guaranteed.^3,4,9,13

Postmortem histologic studies have revealed an inflammatory infiltrate within the wall of embolized aneurysms,¹⁶ and this is likely to have a correlate in the form of wall enhancement on gadolinium-enhanced MR imaging studies.⁷ Partly as a result of these observations, there is increasing emphasis on the significance of inflammation within the aneurysm wall and its relationship with the surrounding environment. A recent study has noted that enhancement is greater and persists for longer in large aneurysms, but it can also be observed in asymptomatic patients, including those treated with bare platinum coils.⁷ In this series of patients treated with different coil types, the authors also observed cases of perianeurysmal edema and hydrocephalus, each following the use of hydrogel-coated coils.

The case we describe is interesting in that a significant clinical event (seizure) occurred following treatment of a relatively small aneurysm (7 mm) with bare platinum coils. Most other radiologic reports of perianeurysmal edema have occurred in larger aneurysms, usually, but not exclusively, with the use of modified coils. It is becoming increasingly apparent that adverse inflammatory reactions, such as perianeurysmal edema are not confined to just 1 coil type and are also observed with bare platinum coils as well as in untreated patients.^3,9 Only by close surveillance of patients treated with modified coils and by rigorous reporting of adverse events will we understand whether the incidence of inflammatory complications is increased, as many believe, by the use of modified platinum coils.