Papillary thyroid cancer

Papillary thyroid cancer is the most common malignancy of the thyroid gland, and accounts for majority (approximately 70%) of thyroid neoplasms ².

Demographics and clinical presentation

Papillary thyroid cancer (as is the case with follicular thyroid carcer) typically occurs in the middle aged with a peak incidence in the 3^rd and 4^th decades. It is more common in women with a F:M ratio of 1:1.6-3:1 ².

Pathology

• characteristic Orphan Annie eye nuclear inclusions
• psammoma bodies
• lymphatic spread is more common than haematogenous spread (c.f. follicular)
• multifocality is common

Papillary carcinoma has a tendency to metastasize early to local lymph nodes, with 50% (39 - 90% ² ) of patients having nodal involvement at presentation ¹ (c.f. 10% for follicular thyroid cancer). These metastases are usually to the ipsilateral jugular chain (87.8%) and are usually confined to the mid and lower lymph node stations, level III and IV (73.2%) ¹.

In approximately 20% of patients lymph node metastases are the first presentation. Distal haematogenous dissemination is less common than with follicular cancer, with only in 5 - 10% of patients at presentation.

Radiographic features

• the so-called lateral aberrant thyroid is actually a lymph node metastasis from papillary thyroid carcinoma

Lymph node metastases

CT

• Involved lymph nodes tend to have ¹:
• cystic components : ~ 35 %
• thick nodular walls : ~ 40 %
• septae : ~ 60 %
• purely cystic nodes are uncommon and more frequent in young patients.
• calcification may be seen occasionally (see case 1)

MRI

MRI, although probably more sensitive that CT, is nonetheless still far from perfect with a sensitivity of only 67% ². This is largely a result of the fact that as many as half involved nodes found histologically following surgery, being less than 3mm in diameter ².

As discussed above, nodes have a tendency to be come cystic. The cystic component will have near-fluid attenuation. The solid metastatic component will appear ²:

• T1
  • hypointense
  • enhancement best seen with fat suppression
• T2 : variable ²
  • hypo intense: 34%
  • iso intense: 45%
  • hyper intense:  21%

Treatment and prognosis

• Surgical
• Radioactive iodine

Overall papillary carcinoma carries a relatively good prognosis with a 20 year survival rate of approximately 90%. If the tumour is confined to the gland then mortality is less than 2.5%, with a sharp increase in mortality in patients with extension beyond the gland, to 38% ².