Neck Mass, Goiter, and Thyroid Disease for MCCQE1

Introduction

The evaluation of a neck mass and thyroid disease is a high-yield topic for the MCCQE1. Candidates are expected to demonstrate competence in the clinical assessment, appropriate investigation, and initial management of neck masses and thyroid abnormalities. This guide focuses on the Medical Council of Canada (MCC) objectives, incorporating the CanMEDS framework and Canadian clinical practice guidelines.

Anatomy and Differential Diagnosis

Understanding the anatomical location of a neck mass is crucial for narrowing the differential diagnosis.

Anatomical Triangles of the Neck

• Anterior Triangle: Bounded by the midline, SCM, and mandible. (Contains thyroid, larynx, lymph nodes).
• Posterior Triangle: Bounded by the SCM, trapezius, and clavicle. (Contains lymph nodes, accessory nerve).

Differential Diagnosis by Location

Approach to Thyroid Nodules

Thyroid nodules are extremely common, detected in up to 50-60% of healthy adults via ultrasound. The primary goal in MCCQE1 scenarios is to distinguish benign nodules from malignancy.

Bethesda System for Reporting Thyroid Cytopathology

Goiter

A goiter is an abnormal enlargement of the thyroid gland.

Etiology in Canada

1. Autoimmune: Hashimoto’s thyroiditis (most common cause of hypothyroidism and goiter in non-endemic areas like Canada), Graves’ disease.
2. Colloid Nodules: Multinodular goiter.
3. Thyroiditis: Subacute (de Quervain’s), Postpartum, Silent.
4. Malignancy.
5. Drugs: Lithium, Amiodarone.

Clinical Evaluation

• Pemberton’s Sign: Instruct patient to raise arms above head. Facial flushing, distended neck veins, or stridor indicates substernal goiter causing thoracic inlet obstruction.
• Obstructive Symptoms: Dysphagia (esophagus), Dyspnea/Stridor (trachea), Hoarseness (nerve).

Management

• Euthyroid Multinodular Goiter: Observation if asymptomatic. Surgery if compressive symptoms or cosmetic concern.
• Toxic Multinodular Goiter: Radioactive Iodine (RAI) or Surgery.

Thyroid Malignancies

Thyroid cancer is the most common endocrine malignancy.

Types of Thyroid Cancer

Canadian Guidelines & Choosing Wisely

Adherence to Choosing Wisely Canada recommendations is essential for the MCCQE1.

1. Don’t order neck ultrasounds for hypothyroidism: In patients with abnormal TSH but a normal neck palpation, ultrasound is generally not indicated as incidentalomas are common and rarely significant.
2. Don’t order T3 for hypothyroidism: TSH is the screening test; Free T4 is the confirmatory test. T3 is preserved until late disease.
3. Don’t routinely order calcitonin: For thyroid nodules unless there is a family history of Medullary Thyroid Cancer or MEN2.

Key Points to Remember for MCCQE1

• Most common cause of neck mass in young adults: Inflammatory (lymphadenopathy) or Congenital (Thyroglossal/Branchial).
• Most common cause of neck mass in patients >40: Malignancy until proven otherwise (Metastatic SCC or Thyroid).
• FNA Limitation: FNA cannot distinguish Follicular Adenoma from Follicular Carcinoma. This requires surgical excision to look for capsular invasion.
• MEN 2 Associations:
  • MEN 2A: Medullary Thyroid Ca, Pheochromocytoma, Parathyroid Hyperplasia.
  • MEN 2B: Medullary Thyroid Ca, Pheochromocytoma, Mucosal Neuromas, Marfanoid habitus.
• CanMEDS Health Advocate: Discussing smoking cessation (risk for Graves’ ophthalmopathy) and screening family members in MEN syndromes.

Sample Question

Case Presentation

A 45-year-old female presents to her family physician with a painless lump in her anterior neck that she noticed while applying makeup. She reports no difficulty swallowing, no voice changes, and no palpitations or tremors. Her past medical history is unremarkable. She has no history of head or neck radiation.

On physical examination, a firm, mobile, 2.5 cm nodule is palpable in the right lobe of the thyroid. It moves with swallowing. There is no palpable cervical lymphadenopathy.

Laboratory investigations reveal:

• TSH: 1.5 mIU/L (Normal: 0.4 – 4.0 mIU/L)

A neck ultrasound is performed, which demonstrates a 2.6 cm solid, hypoechoic nodule with irregular margins and microcalcifications in the right thyroid lobe.

Question

Which one of the following is the most appropriate next step in management?

• A. Repeat TSH in 6 months
• B. Thyroid Scintigraphy (Radioiodine Scan)
• C. Fine Needle Aspiration (FNA) biopsy
• D. Measurement of serum Thyroglobulin
• E. Referral for immediate Hemithyroidectomy

Explanation

The correct answer is:

• C. Fine Needle Aspiration (FNA) biopsy

Explanation: This patient presents with a thyroid nodule. The initial step in evaluation is TSH measurement. Since the TSH is normal (1.5 mIU/L), the nodule is non-functioning (not “hot”), and the risk of malignancy must be assessed via Ultrasound (US) and potentially FNA.

According to Canadian and international guidelines (such as ATA and ACR TI-RADS), a nodule that is solid, hypoechoic, and contains microcalcifications is highly suspicious for malignancy (specifically Papillary Thyroid Carcinoma). Furthermore, the nodule is >1 cm. Therefore, a tissue diagnosis via Fine Needle Aspiration (FNA) is the mandatory next step to guide management.

• Option A: Observation is inappropriate for a nodule with suspicious ultrasound features of this size.
• Option B: Thyroid Scintigraphy is indicated only if the TSH is suppressed (low) to rule out a toxic adenoma. It has no role when TSH is normal.
• Option D: Serum Thyroglobulin is a tumor marker used for monitoring recurrence after thyroidectomy for differentiated thyroid cancer. It is not a diagnostic test for thyroid nodules as it can be elevated in benign conditions.
• Option E: Surgery may eventually be required, but it is not the immediate next step. A diagnosis via FNA is required first to plan the extent of surgery (e.g., hemithyroidectomy vs. total thyroidectomy + lymph node dissection).

References

1. Medical Council of Canada. (n.d.). Objectives for the Qualifying Examination Part I. Retrieved from mcc.ca 
2. Choosing Wisely Canada. (n.d.). Endocrinology and Metabolism. Retrieved from choosingwiselycanada.org 
3. Toward Optimized Practice (TOP) Alberta. (2020). Investigation and Management of Thyroid Nodules.
4. American Thyroid Association (ATA). (2015). Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer.
5. Toronto Notes. (2023). Otolaryngology & Endocrinology Sections.