Refractory in-stent stenosis after flow diverter stenting associated with delayed cobalt allergic reaction

J Neurointerv Surg. 2022 Apr;14(4):e4. doi: 10.1136/neurintsurg-2021-017948. Epub 2021 Aug 25.


In-stent stenosis (ISS) triggered by a metal-induced allergic reaction of Pipeline embolization device (PED) placement is extremely rare. The present report describes a patient who presented with delayed parent artery occlusion and refractory ISS after PED placement due to cobalt allergy. A patient in her 70s underwent PED placement for a right internal carotid artery (ICA) large aneurysm; 4 months later, the patient presented with left-sided hemiparesis, and MRI revealed right ICA occlusion even though antiplatelet therapy was optimal. She underwent mechanical thrombectomy, and successful recanalization was achieved. However, follow-up angiography 6 months after the thrombectomy revealed severe ISS, and the patch testing showed a positive reaction for cobalt. As a result of long-term administration of oral steroids and antihistamine, progression of ISS was suppressed. It was supposed that a delayed hypersensitivity reaction to cobalt might induce refractory ISS after PED placement.

Keywords: angioplasty; flow diverter; inflammatory response; thrombectomy.

MeSH terms

  • Carotid Artery, Internal
  • Cobalt / adverse effects
  • Constriction, Pathologic / complications
  • Embolization, Therapeutic* / adverse effects
  • Female
  • Humans
  • Hypersensitivity* / complications
  • Hypersensitivity* / etiology
  • Intracranial Aneurysm* / therapy
  • Stents / adverse effects


  • Cobalt