Introduction
Appropriately treated differentiated thyroid cancer (DTC) confers an excellent 10-year survival rate of over 90% for both papillary and follicular carcinoma1.  However up to 30% of patients experience loco-regional recurrence within 10 years of diagnosis.
The routine use of post-treatment ultrasound (US) surveillance and thyroglobulin assay allows for early detection of non-palpable recurrent disease. Treatment options include radioiodine ablation or further surgical intervention; the former is limited to sub-centimetre lesions that exhibit radioiodine uptake. Recurrent disease may be iodine negative i.e. dedifferentiated in up to 30% of patients and may persist despite ablative treatment 3. For these cases, surgical excision remains the mainstay of treatment.
The localisation of recurrent disease and identification of important structures to be preserved in previously dissected necks is challenging due to the presence of fibrotic scar tissue, neovascularisation and modified anatomy. The complication rates for transient and persistent hypoparathyroidism and recurrent laryngeal nerve injury are reportedly significantly higher in secondary vs primary surgery3.
Various techniques are employed for pre-operative localisation of non-palpable lesions in patients with cytologically proven recurrent DTC (rDTC) in the neck. These include intra-operative US guidance, I131 guided gamma probe and Methylene blue dye.
The use of charcoal tattooing for identification of recurrence of malignancy is well established in secondary breast surgery where it has been shown to be both safe and effective4 and in recent years, has been shown to be successful in the surgical management of rDTC5,6.
We aim to inform the readership of the technical aspects of using activated charcoal suspension injection for the localisation of DTC in the neck of previously treated patients based on our experience at [removed for blind peer review].