Diagnosis of Papillary Cancer (PTC)
The diagnosis of PTC is made by a combination of careful clinical assessment, ultrasound and FNA cytology, and generally follows the pattern I have outlined in greater detail on the webpage for Thyroid nodules.
I have also created a booklet, outlining the steps in diagnosis and treatment of thyroid cancer, which can be found on the webpage Guide to Surgery.
Fig.1: Cytology of PTC showing crowded overlapping nuclei & intranuclear holesInitial workup of a thyroid nodule includes FNA cytology (needle test) of the lump in the thyroid and possibly of an enlarged lymph node if present (Fig. 1).
FNA Cytology +/- Thyroglobulin Wash
Cytology is relatively painless, can be performed with or without local anaesthesia, and should be performed under ultrasound control to improve diagnostic accuracy. Cytology should be done on suspicious thyroid nodules and any enlarged and potentially involved lymph nodes.
The results of thyroid FNA should always be interpreted in the light of the clinical findings. Clinically suspicious nodules should be regarded as malignant despite negative cytology, until histological diagnosis has been confirmed.
An aid to diagnosis of lymph node metastases is to perform FNA of suspicious lymph nodes with thyroglobulin wash. This measures the thyroglobulin level in the needle sample from the node, which should be zero. If it is elevated however, this indicates the node contains metastatic tumour.
Ultrasound
Ultrasound will also aid diagnosis, with marked hypoechogenicity, irregular or microlobulated margins, a taller-than-wide shape, and microcalcifications in a nodule suggesting malignancy (Fig. 2). Ultrasound is not a substitute for good FNA cytology however, which must always be performed.
Fig.2: Ultrasounds of the thyroid showing PTC with irregular margin and lobulations (left), PTC affected lymph nodes in the neck (centre) and US guided plan of PTC involved nodes in the neck (right)Ultrasound can also be extremely useful in assessing the neck for the presence of lymph nodes that may be involved with tumour, either before the primary operation or in subsequent followup. It can be used to map the site of nodes on the skin prior to surgery, especially when the glands are difficult to feel or are in deeper positions.
Fig.4: MRI scan of PTC disease in thyroid and nodes (arrowed)CT or MRI
Since US evaluation is operator dependent and cannot always adequately image deeper structures and those areas behind bone or trachea (in an acoustic shadow), alternative cross-sectional imaging with CT or MRI may be more useful as an adjunct in some clinical settings (Figs 3 & 4).
Patients displaying bulky or widely distributed nodal disease on initial US examination may present with involvement of nodal regions beyond the typical cervical regions, some of which may be difficult to visualise on routine preoperative US, including the mediastinum, infraclavicular, retropharyngeal, and parapharyngeal regions.
Fig. 3: CT scan of the neck with grossly enlarged PTC lymph nodes visible in the R neck (arrowed).
Neck CT & MRI are very useful in demonstrating local invasion of other structures in the neck such as larynx, trachea or oesophagus, especially when there are symptoms of aggressive local disease. These signs and symptoms will include progressive dysphagia, respiratory compromise, haemoptysis, rapid tumour enlargement, significant voice change or the finding of vocal cord paralysis, and mass fixation to the airway or neck structures.
CT will also delineate bulky nodal disease, which may harbour significant extranodal extension that involves muscle and/or blood vessels. Preoperative knowledge of these features of the primary tumour or metastases could significantly influence the surgical plan.
It is also very helpful in mapping disease recurrence in lymph nodes prior to redo surgery, allowing the surgeon to minimise the extent of dissection required and therefore the potential risk of complications.
The use of IV contrast is an important adjunct because it helps to outline the anatomical relationship between the primary tumour or metastatic disease and other structures. Modern contrast media do not cause a problem with iodine 'stunning' of cells. But even if iodine contrast is used, it is generally cleared within 4–8 weeks in most patients, so concern about iodine burden from IV contrast causing a clinically significant delay in subsequent whole-body scans (WBSs) or RAI treatment after the imaging followed by surgery is generally unfounded.
PET scan or radioiodine scan
Fig. 5: PET scan with PTC recurrence (arrowed)Nuclear imaging may be required to detect occult recurrent disease in the neck or elsewhere, but is generally only used after initial surgery during the followup period or prior to radioiodine therapy. It is not recommended for use in the initial workup of the patient (Fig. 5).
FDG-PET scanning is most useful in evaluating the patient's response to therapy, and whether further surgery might be required or possible treatment with radioactive iodine. This is used as an adjunct to allow dynamic risk stratification, where the management evolves over time as investigation and treatment goes on.
This might result in a change in surveillance frequency, adjustments to the level of TSH suppression, or identifying the need for further imaging (e.g. with a rising thyroglobulin level).
Endoscopy
Laryngoscopy may be useful, especially in the investigation of voice changes prior to surgery, which may indicate invasion of the recurrent laryngeal nerve, trachea or larynx.
Oesophagoscopy may also be indicated if there is any suggestion of invasion on cross-sectional imaging.