title: Calcium hydroxyapatite crystal deposition with intraosseous penetration involving the posterior aspect of the cervical spine: a previously unreported cause of neck pain.
abstract: Calcific tendinitis is a frequent disorder caused by hydroxyapatite crystal deposition; however, bone erosions from calcific tendinitis are unusual. The spinal manifestation of this disease is calcific tendinitis of the longus colli muscle; this disease has never been described in the posterior aspect of the spine. We report a case of calcium hydroxyapatite crystal deposition involving the posterior cervical spine eroding the bone cortex.
  
  
  
  A 57-year-old woman presented with a 5-month history of left-sided neck pain. Radiographs showed C4-C5 interspinous calcification with lytic compromise of the posterior arch of C4. Magnetic resonance imaging confirmed a lytic lesion of the posterior arch of C4, with a soft tissue mass extending to the C4-C5 interspinous space; calcifications were observed as very low signal intensity areas on T1 and T2 sequences, surrounded by gadolinium-enhanced soft tissues. A computed tomography (CT) scan confirmed the bone erosions and the soft tissue calcifications.
  
  
  
  A CT-guided needle biopsy was performed; it showed vascularized connective tissue with inflammatory histiocytic infiltration and multinucleated giant cells; Alizarin Red stain confirmed the presence of hydroxyapatite crystals. The patient was treated with anti-inflammatories for 2 weeks. She has been asymptomatic in a 6-month follow-up; a CT scan at the last follow-up revealed reparative remodeling of bone erosions.
  
  
  
  This is the first report of calcium hydroxyapatite crystal deposition with intraosseous penetration involving the posterior aspect of the cervical spine. Considering that this unusual lesion can be misinterpreted as a tumor or infection, high suspicion is required to avoid unnecessary surgical procedures.
authors: Department of Orthopaedic Surgery, School of Medicine, Pontificia Universidad Catolica de Chile, Marcoleta 352, Santiago, Chile. jurrutia@med.puc.cl.
authors: Julio
authors: J
authors: Urrutia
authors: Department of Radiology, School of Medicine, Pontificia Universidad Catolica de Chile, Santiago, Chile.
authors: Oscar
authors: O
authors: Contreras
mesh_terms: D002114:Calcinosis / Q000150:complications*; D002574:Cervical Vertebrae / Q000473:pathology*; D017886:Durapatite / Q000378:metabolism*; D005260:Female; D006801:Humans; D008875:Middle Aged; D019547:Neck Pain / Q000209:etiology*; D052256:Tendinopathy / Q000150:complications*
chemical_list: D017886:Durapatite
keywords: Calcific tendinitis; Cervical spine; Crystal deposition disease; Hydroxyapatite; Neck pain