ABSTRACT Objective: Cervical traumatic neuromas (CTNs) may appear after lateral neck dissection for metastatic thyroid carcinoma. If they are misdiagnosed as metastatic lymph nodes (LNs) in follow-up neck ultrasound (US), unnecessary and uncomfortable fine-needle aspiration biopsy are indicated. The present study aimed to describe US features of CTNs and to assess the US performance in distinguishing CTNs from abnormal LNs. Subjects and methods: Retrospective evaluation of neck US images of 206 consecutive patients who had lateral neck dissection as a part of thyroid cancer treatment to assess CTN’s US features. Diagnostic accuracy study to evaluate US performance in distinguishing CTNs from abnormal LNs was performed. Results: Eight-six lateral neck nodules were selected for analysis: 38 CTNs and 48 abnormal LNs. CTNs with diagnostic cytology were predominantly hypoechogenic (100% vs. 45%; P = 0.008) and had shorter diameters than inconclusive cytology CTNs: short axis (0.39 cm vs. 0.50 cm; P = 0.03) and long axis (1.64 cm vs. 2.35 cm; P = 0.021). The US features with the best accuracy to distinguish CTNs from abnormal LNs were continuity with a nervous structure, hypoechogenic internal lines, short/long axis ratio ≤ 0.42, absent Doppler vascularization, fusiform morphology, and short axis ≤ 0.48 cm. Conclusion: US is a very useful method for assessing CTNs, with good performance in distinguishing CTNs from abnormal LNs.

SUMMARY Collision tumors are rare and may comprise components with different behavior, treatments, and prognosis. We report an unprecedented case of aggressive thyroid collision tumor containing widely invasive oncocytic carcinoma (OC), classical and hobnail (HPTC) variants of papillary carcinoma, and poorly differentiated carcinoma (PDTC). The patient underwent total thyroidectomy, radioactive iodine therapy, and within months progressed with local recurrence, and pulmonary metastases requiring neck dissection, external radiotherapy and systemic treatment with sorafenib. The rapid progression, dedifferentiated metastatic lesions, and failure to treatments resulted in the patient´s death. The great variety of histological types and the evolution of this case were a challenge for the management of metastatic disease. Widely invasive OC, HPTC and PDTC are considered to have a worse prognosis. HPTC has never been reported as a component of a collision tumor. HPTC and PDTC should call attention to a possible higher-grade transformation.