Neck Mass With Progressive Shortness of Breath

Awoman in her 40s presented with progressive dyspnea and inability to lie flat. Two years prior to presentation, she had noticed a tender, firm thyroidenlargementassociatedwith rapidweightgain. She was hypothyroid with a thyroid-stimulating hormone level of 15.42mIU/Landa free thyroxine levelof0.95ng/dL. (Toconvert free thyroxine topicomolesper liter,multiplyby 12.871.) Shewas started on treatmentwith levothyroxine. Thyroid fine-needle aspiration revealedfibrosisandmixed inflammatorycells,andexaminationofcore biopsy specimen showed sclerosis and chronic inflammation. She was followed closely by an endocrinologist and treated with maximal medical therapy over 2 years without improvement. Computed tomographywithout contrast at the timeofpresentationdemonstrated trachealnarrowing to 1.56mm(Figure, A). Tracheostomywas recommendedwith the possibility of subtotal thyroid resectionpendingfeasibilityduringsurgery. Intraoperatively, the thyroid glandwas fibrotic and scarred to the anterior tracheal wall, sternothyroid, prevertebral fascia, and jugular vein. The recurrent laryngeal nerve (RLN)was encased in firm, fibrotic tissue requiring extensive dissection and reflection of the gland frommedial to lateral over the nerve. Total right thyroid lobectomywas successfully performedwithRLNpreservation, resulting in immediate improvement in airway caliber. Tracheostomy was not performed. Flexible laryngoscopy demonstrated normal vocal cord function at the first postoperativevisit, and thepatient’s dyspneaand inability to lay supine had completely resolved. Grossly, thespecimenwas tan, firm,and fibrotic.Theentire lobe appeared tobe involved in thediseaseprocess.Histopathologic examination revealed obliterative fibrosis and chronic inflammation (Figure,B). Immunohistochemical stains for total IgGand IgG4demonstrated increased IgG4-positive plasma cells (Figure, C). In addition, entrapped benign parathyroid tissue was noted (Figure, D). What is your diagnosis? A B