Clinical, CT, and MRI Features of Acute Calcific Tendinitis of the Longus Colli: A Case Series with Novel Imaging Findings.

Objective: To evaluate the clinical and radiologic features of acute calcific tendinitis of the longus colli (ACTLC).

Methods: This retrospective, cross-sectional study analysed 30 patients diagnosed with ACTLC from January 2013 to December 2022. Two experienced radiologists independently reviewed CT and MR images to confirm the ACTLC diagnosis and document radiologic findings. Clinical data, including symptoms and laboratory results, were also assessed. The study received approval from the institutional ethics committee, with patient consent waived.

Results: The cohort had a mean age of 49 years and included 19 females (63%). All patients presented with acute cervicalgia, and 29 (97%) exhibited calcifications at the C1-C2 level. A novel imaging feature, termed the "beak sign," was observed in 24 of these 29 patients (83%), defined by an acute angle at the margin of calcification pointing toward the C1-C2 intervertebral space. Prevertebral soft-tissue oedema was present in all patients, with 25 (83%) also showing retropharyngeal fluid accumulation. Among the 14 patients who underwent MRI, 11 (79%) exhibited atlantoaxial joint effusion, a feature rarely reported in ACTLC. Follow-up imaging revealed inferior migration of calcifications in two patients, with one developing a cyst-like appearance in the post-calcific phase-an unreported finding in ACTLC.

Conclusions: This study represents the largest ACTLC cohort confirmed by cross-sectional imaging. Prevertebral calcifications and soft-tissue oedema were consistently observed in all patients, with the majority also exhibiting retropharyngeal fluid accumulation. This article introduces the "beak sign," a novel imaging finding observed in most cases, and identifies atlantoaxial joint effusion as a newly recognised, common imaging manifestation in ACTLC.