This article reports a case of an elderly female who presented with instability in standing and walking. She had a long-term vegetarian diet and experienced nutritional deficiency in the three months preceding onset. Cervical spinal MRI revealed an "inverted V sign" in the posterior columns. Based on the patient's symptoms, signs, auxiliary examinations, and treatment follow-up results, a final diagnosis of subacute combined degeneration was made. By reviewing the pathophysiological mechanism of the "inverted V sign" as a distinctive imaging manifestation, this article explores the differential diagnostic considerations for this radiological finding.