Teaching Case

41-year-old female patient referred by her GP for a CT of the C-spine due to a complaint of chronic neck pain.

CT of the C-spine demonstrates an incidentally found 12x11 mm nodule in the right lobe of the thyroid with punctate calcifications within. No additional thyroid nodules or regional lymphadenopathy was noted.

Sonography confirms a 1.2 cm diameter right upper pole thyroid nodule. It is circumscribed with central solid and peripheral cystic components. The solid component is vascular. There are multiple punctate echogenic foci throughout the nodule.

70% of normal thyroids contain nodules detectable on ultrasound [1], but only 4-7% of these are at risk for thyroid cancer--its incidence is 9/100, 000 [2], and it accounts for only 1% of all cancers [3]. Hence, nodules are a common finding, but most are benign. Yet, the incidence of papillary thyroid cancer has more than doubled in recent times--largely due to increasing detection [4]. Differentiated thyroid carcinoma, which includes the papillary and follicular subtypes, peaks in the third and fourth decades and is three times as common in females [5]. It is generally sporadic, although more common following exposure to radiation [6].

Papillary thyroid carcinoma most often presents as a nontender palpable nodule [3]. It may cause hoarseness, cough, and dysphagia [6]. Thyroid nodules are common and are nearly always benign [7] but do carry the potential for malignancy, and so imaging is necessary to better characterise them. Red flags include a family history of thyroid cancer, a history of radiation exposure, cervical lymphadenopathy, persistent pain, and rapid enlargement [1]. It typically spreads to local cervical nodes and haematogenously to lung, bone, and the CNS [6].

Thyroid nodules may present as incidental findings on CT, but this modality cannot reliably distinguish malignant from benign lesions [8]. Thyroid carcinoma is highly variable: it may involve single or multiple nodules, may be well-circumscribed or ill-defined, solid or cystic, and may or may not have calcifications [5]. Generally, tumours are hypodense compared to the gland and do include calcifications [6]. Calcification of cervical nodes should raise suspicion of papillary carcinoma, which has a propensity for lymphatic spread [2]. CT is best utilised to identify extrathyroidal invasion [2] and for staging [5]. Sonography is the modality of choice for thyroid nodules [1] and detects nodules as small as 0.2 cm [4], but even it can seldom distinguish carcinoma from adenoma [6]. Thyroid malignancy will frequently appear ill-defined and hypoechoic [5] with fine punctate calcifications and intranodular flow on Doppler [7].

Nodules 1 cm or larger are generally biopsied by FNA, and ultrasound guidance is preferable [6]. The prognosis for papillary thyroid carcinoma is excellent--96% survive at 10 years [6]. Treatment involves at least a partial thyroidectomy and may utilise I-131 ablation and radiation therapy in advanced disease [6].

Thyroid carcinoma is a frequent worry but rare diagnosis. Imaging is good at detecting thyroid lesions but poor at distinguishing malignancy from benignity--a biopsy is often needed.