Introduction
Giant-Cell Arteritis (GCA), or Horton’s disease, is a granulomatous vasculitis affecting the large and medium arteries, especially involving the extracranial branches of the carotid arteries, in particular, the temporal artery (1) which was first described by Hutchinson in 1890 and by Horton et al in 1932 (2). The incidence of GCA increases with age and almost exclusively affects patients over 50 years of age or older and is more frequent in women (3). Common symptoms are new-onset headache, scalp tenderness, jaw claudication, fever, asthenia, weight loss and polymyalgia rheumatica (3). GCA may be responsible of sudden irreversible bilateral vision loss  and remains a medical emergency (3,4).
Temporal artery biopsy (TAB) plays an important role to confirm GCA diagnosis. Common histological features are the presence of macrophages and lymphocytes infiltrates and multinucleated giant cells (5).
According to the American College of Rheumatology (ACR) 1990 criteria for the classification of GCA, 5 criteria were selected for the diagnosis: age ≥ 50 years at disease onset, new onset of localized headache, temporal artery tenderness or decreased temporal artery pulse, elevated erythrocyte sedimentation rate ≥  50 mml/hour, and biopsy sample including an artery, showing necrotizing arteritis, characterized by a predominance of mononuclear cell infiltrates or a granulomatous process with multinucleated giant cells. At least 3 of these 5 criteria are needed for GCA diagnosis (6).
However, histological characteristics in GCA are various with multiple terms and definitions making diagnosis sometimes difficult because of variability of patterns and the coexistence of different patterns in a same artery (5). Hernandez-Rodriguez described and validated 4 histological patterns of TAB from GCA patients with the proposal of a dynamic model of arterial invasion reflecting the progression of inflammation and damage. These 4 patterns are : 1- adventitial ; 2- adventitial invasive (adventitial involvement with some extension to the muscular layer) ; 3- concentric bilayer (adventitial and intimal involvement with media layer preservation ; 4- panarteritic (5).
We here describe the case of a 51-year-old man with TAB showing lymphocytes infiltrates in the adventitia suggestive of an adventitial pattern of GCA according to Hernandez-Rodriguez et al.