False positive helmet sign on radioactive iodine-131 scintigraphy

Abstract

379 Indian Journal of Cancer | Volume 56 | Issue 4 | October-December 2019 False positive helmet sign on radioactive iodine‐131 scintigraphy A 40 year old woman with no comorbid i l lnesses was referred to our center for further management of papillary carcinoma of the thyroid. Clinical examination along with ultrasound correlation revealed thyromegaly with multiple hypoehoic nodules, the largest being a 3 cm complex nodule involving the left thyroid lobe and also multiple enlarged left lateral neck nodes that were cytology-proven to be metastatic papillary carcinoma of the thyroid. She underwent an uneventful total thyroidectomy with central compartment neck dissection and left functional neck dissection. Her postoperative histology confirmed the diagnosis of multicentric conventional papillary carcinoma thyroid with minimal extrathyroidal extension. Two central compartment neck nodes and three out of the 20 left lateral neck nodes were positive for metastatic papillary carcinoma with perinodal spread. Her postoperative diagnostic Iodine 131 scan showed local uptake of 2%; her whole body scan was however negative. [Figure 1a] Her postoperative serum thyroglobulin was 0.36, the anti-thyroglobulin antibody was within normal limits. She was subsequently taken up for radioactive Iodine ablation with 55 millicuries of Iodine-131. Her post-therapy scan apart from the local uptake revealed the classical “Helmet Sign,” an artifact caused by diffuse tracer accumulation in the patient’s scalp most possibly related to her recent hair dyeing as corroborated with the patient’s clinical history. [Figure 1b] This artifact was considered disease-unrelated, taking into account the patient’s history, normal levels of serum thyroglobulin throughout and the reduction (Post therapy scan Day 11 [Figure 1c] scan done after a hair wash with a medicated shampoo), and subsequent disappearance of the diffuse increased scalp activity in the follow-up Iodine-131 scans after 6 months. She continues to be disease-free on thyroxine suppression and has normal serum thyroglobulin for over 2 years now.