Pictorial ultrasound reports combined with fine needle washout thyroglobulin assay to aid thyroid surgery

Authors


  • The authors have no funding, financial relationships, or conflicts of interest to disclose.

INTRODUCTION

Thyroid carcinoma patients, despite their generally excellent prognosis, have cervical nodal involvement at presentation in approximately 35% to 40% of cases. Furthermore, the vast majority of the 5% to 20% of recurrences are of a locoregional nature. 1 Ultrasound (US) is commonly employed for both diagnosis and staging of the thyroid and cervical lymph nodes. The cytology of suspicious nodes or thyroid nodules can then be verified by fine needle aspiration (FNA) cytology. US guidance of FNA increases the number of representative samples as compared to non-US guided FNA. 2 If the node is not palpable the US report is used to guide the surgeon to its location. A text description of the location of pathology typically involves mentioning the anatomical location (Union Internationale Contre le Cancer) or numeric level (American Joint Committee on Cancer). 3 Although useful, descriptive methods are far from a definitive way of localizing the abnormality. Still pictures from the dynamic US scan are rarely helpful as a surgical map as they are normally only interpretable by the ultrasonographer.

Cases of recurrent thyroid carcinoma are usually managed with radioiodine for small volume, iodine-avid disease or surgery with or without radioiodine for macroscopic cervical recurrence. The operation, as with surgical resection of primary disease, can be highly selective but is dependant on accurate preoperative disease localization. This is usually with iodine uptake scans and US. We describe how we use a simple sketch drawing to aid lymph node localization during therapeutic neck dissections for thyroid carcinomas. We also explain how we employ thyroglobulin assays from FNA samples in recurrent cases to enhance preoperative planning.

TECHNIQUE FOR CERVICAL STAGING OF NEWLY DIAGNOSED THYROID CARCINOMA

New presentations of suspected thyroid carcinoma not only have ultrasound of both lobes of the thyroid itself but also both sides of the neck. There are several features of lymph nodes that alert the ultrasonographer to an increased likelihood of malignancy within a lymph node. These include round shape, short axis diameter >8 mm, heterogeneous echotexture, cystic or necrotic areas, fatty hilum, ill-defined margins, and invasion of surrounding tissue. 4 FNA cytology of the thyroid and suspicious cervical areas under ultrasound guidance is performed. A simple line drawing of the nodal map of the neck is then sketched with suspicious nodes crosshatched, and the areas from which cytological aspirates were taken are indicated. This produces an easily interpretable picture to use as a surgical map (Fig. 1).

Figure 1.

Example of an ultrasound report indicating areas of suspicion and corresponding fine needle aspiration (FNA) sites.

TECHNIQUE FOR SUSPECTED RECURRENCE OF THYROID CARCINOMA

Recurrence of differentiated thyroid cancer usually presents as either a rising serum thyroglobulin (stimulated or nonstimulated) or as a cervical node. Once the patient has had the thyroid removed the technique of US and FNA can be further enhanced by performing a thyroglobulin (Tg) assay on the washout fluid from the needle. There is 1 mL of normal saline used to rinse the needle out after FNA cytology. This rinse fluid is sent for Tg assay and considered positive if it is at a higher level than the patient's serum Tg. This is combined with the schematic drawing and FNA cytology to form a nodal map of the recurrence.

DISCUSSION

When a highly selective neck dissection is planned for either the primary treatment or recurrence of differentiated thyroid cancer, the exact location of nodal disease or abnormality is of paramount importance to avoid unnecessary tissue handling and associated surgical time and morbidity. We feel that the simple schematic drawing allows for a more thorough surgical clearance of pathology while minimizing unnecessary dissection. Another advantage of the technique is the reduced requirement for cross-sectional imaging such as noncontrast computed tomography and MRI. The option of earlier radioiodine therapy was at the cost of lack of tissue differentiation without iodine-based contrast mediums.

The technique of FNA washout Tg assay is mainly employed for recurrent disease cases in post-thyroidectomy patients as opposed to primary cases when there is a thyroid gland present. This is due to the chance of aspirate containing just blood and therefore an elevated Tg aspirate being due to the raised serum Tg and not because a secondary deposit had been localized. This is less of a problem in post-thyroidectomy patients as the total Tg is typically lower once the primary tumor and remaining thyroid has been resected and or ablated. When the FNA Tg from a morphologically suspicious node is at a higher concentration than the serum Tg, there is a positive predictive value of 100% that the node contains metastatic differentiated thyroid carcinoma. 5

Other techniques have been employed to aid the surgeon in localizing cervical pathology. One such example is tattooing the skin during US. 6 This can still be done in conjunction with this mapping technique, but the location of small abnormal nodes is rarely helped by a skin mark on an elevated flap within the 3-dimensional neck.

The long natural history of thyroid cancer makes outcome data notoriously difficult to ascertain. Although the immediate and short -term outcomes in the form of reduced thyroglobulin levels and distribution of radioiodine are encouraging, we make no claims as to reduced recurrence or improved disease-specific survival from this technique. These techniques are operator dependant and would require a highly trained neck ultrasonographer. With their help it would be relatively easy to instigate in radiology units by providing a photocopied schematic diagram of the neck with the US request form. We also employ this technique for parathyroid disease.

CONCLUSION

A picture tells a thousand words.

Ancillary