Case Report Perianeursymal Cyst Development after Endovascular Treatment of a Ruptured Giant Aneurysm Ramesh Grandhi, MD, Robert A. Miller, MD, Nathan T. Zwagerman, MD, L. Dade Lunsford, MD, Michael Horowitz, MD From the University of Pittsburgh Medical Center – Neurological Surgery, Pittsburgh, PA (RG, RAM, NTZ, LDL); Pennsylvania Brain and Spine Institute, Pittsburgh, PA (MH). Keywords: Perianeursymal cyst, endovascular embolization, stereotactic cyst aspiration, intracavitary irradiation. Acceptance: Received September 28, 2012, and in revised form December 26, 2012. Accepted for publication December 26, 2012. Correspondence: Address correspondence to Nathan Zwagerman, University of Pittsburgh Medical Center – Neurological Surgery 200 Lothrop St. B400, Pittsburgh, PA 15213, USA. E-mail: zwagermannt@upmc.edu. Conflict of Interest: None. J Neuroimaging 2014;24:515-517. DOI: 10.1111/jon.12018 History A 51-year-old right-handed man presented with a Hunt & Hess grade 2, Fisher grade 3 subarachnoid hemorrhage in January 2009 and subsequently underwent endovascular treatment of a ruptured 27 mm right internal carotid artery bifurcation aneurysm using a Codman Enterprise vascular reconstruction device (Codman Neurovascular; Raynham, MA, USA) and Axium TM platinum coils (Covidien; Irvine, CA, USA) (Figs 1 and 2). The patient underwent periodic posttreatment an- giograms to screen for aneurysm regrowth. Over 3 years, the patient had four additional coil embolizations. In March 2012, he presented with progressively worsening headaches. Examination The patient’s examination revealed a mild left hemiparesis with 4/5 strength in his left upper extremity and 4+/5 strength in his left lower extremity muscle groups. He exhibited a left upper extremity pronator drift and had normal strength on his right side. A head CT revealed the presence of a 4 cm × 5 cm low attenuation cystic lesion in the right basal ganglia (Fig 3), which had not been present 6 months prior. Operation/Pathology/Postoperative Course In order to decompress the cyst and relieve symptoms caused by the lesion’s mass effect, the patient underwent an awake, stereotactic cyst aspiration using a Leksell Stereotactic G-Frame (Elekta AB, Stockholm, Sweden). A total of 35 mL of straw- colored fluid was aspirated from the cyst. The cytologic anal- ysis of the aspirate revealed no cells, but a protein content of 5,000 mg/dL. The patient was discharged home a few days af- ter cyst drainage. The only neurologic deficit that remained was minimal left arm pronation. A repeat head CT performed 4 weeks later demonstrated cyst recurrence. The patient was readmitted for stereotac- tic needle aspiration of the cyst followed by intracavitary phosphorus-32 ( 32 P) radioisotope implantation. Prior to 32 P implantation, contrast was injected into the cyst. No com- munication with the ventricular system was identified. The surgery proceeded without complication and the patient was discharged home with no new neurological deficits. Follow- up imaging at 2 months demonstrated no further cyst enlarge- ment and the patient continues to exhibit minimal left-sided weakness. Discussion Intraparenchymal perianeurysmal cysts are rare. Marcoux et al first described a case in which an arachnoid cyst developed after coil embolization of a ruptured aneurysm. The patient presented with symptoms related to the cyst 17 months af- ter treatment of her anterior communicating artery aneurysm. The patient required two craniotomies to decompress the cyst. 1 A subsequent report by Friedman and colleagues detailed the clinical history and treatment course of a patient with an un- ruptured 13 × 18 mm basilar trunk aneurysm that was treated by coil embolization and placement of a neck remodeling de- vice. Repeat embolization was performed 7 months later to treat residual aneurysm. Thirteen months following the first procedure, the patient developed a symptomatic pontine and lower midbrain cyst. The patient required placement of a ven- triculoperitoneal shunt and a craniotomy for cyst fenestration. Subsequently, the patient underwent another operation for a cysto-peritoneal shunt. 2 Previous authors have suggested a number of different ex- planations for the development and subsequent growth of pe- rianeurysmal cysts. Proposed mechanisms include: (1) clin- ical or subclinical bleeding events, (2) subclinical ischemic Copyright ◦ C 2013 by the American Society of Neuroimaging 515