Horner syndrome associated with contusion of the longus colli muscle simulating a tumor.

A 22-year-old man who was discovered unarousable after an accidental methadone overdose complained of worsening neck pain and left arm weakness over the next week. Examination disclosed a left Horner syndrome and a left brachial plexopathy. Imaging showed a left paraspinal mass adjacent to the sympathetic pathway at the fourth and fifth cervical vertebral levels with imaging features of a tumor. Biopsy was deferred. One month later, the imaging abnormality had nearly disappeared. In retrospect, it represented a contusion injury of the longus colli muscle, a finding not reported previously. Whether it caused the Horner syndrome or was merely a bystander in cervical neck trauma is uncertain. This abnormality should be recognized as a diagnostic confounder.