By Dr Stuart Kidgell and Chantale Mitchell (Specialist Ultrasonographer)
The accidental diagnosis of a thyroid lump during unrelated imaging of the neck is a source of great anxiety for the patient and doctor. Improved imaging quality and increased use of cross sectional imaging has resulted in an ever-increasing quoted incidence of thyroid nodules. The thyroid gland is visualised on MRI and CT scanning of the neck, chest and spine as well as on ultrasound examinations of the neck for other conditions involving the soft tissues, vessels and salivary glands. Up to 20 % of patients, having an MRI or CT scan of the neck will have an accidental diagnosis of a thyroid nodule and up to 66 % of patients having ultrasound of the neck will have an accidental diagnosis of a thyroid nodule. Almost all of these patients will have no symptoms.
The thyroid gland is also obvious in its anatomical location, sitting on the front of the neck. Identification of nodules whilst shaving, applying make-up or during general medical examinations at the doctors’ rooms also accounts for nodules or swellings which require identification to allay the fear of cancer. The incidence of thyroid nodules by clinical evaluation is 5% but the incidence of thyroid nodules combined with radiological imaging is as much as 70% by the age of 70 years.
The incidence of thyroid cancer is very low despite the high incidence of thyroid nodules. Many thyroid cancers in older patients are slow growing and will be present until death rather than being the cause of death.
The challenge for the patient and their doctor is deciding which nodule requires further investigation in view of the fear of cancer. An imaging technique is required which is cost effective, widely available, involves the least risk to the patient and is most accurate in guiding the patient and the referring doctor to the next step. Absolute exclusion of cancer requires some form of cell diagnosis, which means some form of tissue biopsy. If all patients with thyroid lumps switched to undergo biopsy, the cost to the medical aids would be extensive, the risk of inaccurate diagnosis would be increased and unnecessary patient discomfort and inconvenience would be enormous.
Ultrasound scanning of the neck has long been the ideal tool for evaluating the thyroid gland because of its absence of radiation, availability at all radiological practices and marked improvement in image quality in the past 10 years. There has been a significant improvement in ultrasound technology as well as improved image processing. This has allowed smaller nodules to be identified in the thyroid gland as well as better characterisation of the nodules.
The downside of better imaging equipment is the identification of more nodules and the potential for greater anxiety exists. This has resulted in a large number of different systems of categorizing nodules in the thyroid gland, in an attempt to identify which nodules can be ignored and which are of concern. There has not been international consensus on which system is best with British, French, Korean and the American Thyroid associations applying emphasis on particular features with resultant complexity and confusion over which nodules require our attention.
The American College of Radiology has been reviewing imaging features in thyroid disease and has proposed a system which allows accurate repeatable assessment of thyroid nodules. They identify features that direct us to ignore, follow-up or biopsy where appropriate. The April 2017 revision of the ACR- TI RADS (Thyroid Imaging Reporting and Data System) classification has provided the most accurate and most reputable method of evaluation of the thyroid gland and thyroid nodules. This system accurately identifies the position of an abnormality in 15 different zones of the gland and assesses the appearance of nodules based on five different characteristics: Composition, Echogenity, Shape, Margin and Echogenic Foci. Based on the findings, a score is calculated and a level is determined based on a range of level 1 as being benign, up to level 5 as being highly suspicious. This system enables the radiologist to recommend to the referring Doctor whether the nodule can be ignored, re-scanned at 1, 3 and 5-year intervals or requires immediate tissue diagnosis by means of a fine needle biopsy.
Lake, Smit and Partners have adopted this system across all our practices as the equipment and expertise is widely available in our radiology practice. In-house training of the ultrasonographers in identification of the important features as well as universal reporting structures for radiologists will allow the referring doctors to confidently manage the numerous patients who have had the accidental diagnosis of thyroid abnormality detected in the course of imaging for other disease.
Below are some real examples of cases we have assessed and graded: