Intraoperative Monitoring in Endocrine Surgery — MCQs
VMA is elevated in which of the following condition?
Best way to localize extra-adrenal pheochromocytoma:
Which of the following changes in voice is not produced as a result of external laryngeal nerve injury post thyroidectomy?
Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
Thyroid storm during surgery is due to?
In surgical stress all hormones are increased except:
Which nerve is most likely injured during a thyroidectomy?
Most sensitive investigation for preoperative localization of abnormal parathyroid glands is
Hypoparathyroidism following thyroid surgery occurs within:
A patient diagnosed with papillary carcinoma of the thyroid underwent a whole-body iodine scan six weeks after surgery, which revealed residual disease. The next best step is:
Intraoperative Monitoring in Endocrine Surgery Indian Medical PG Practice Questions and MCQs
Question 1: VMA is elevated in which of the following condition?
- A. Tuberous sclerosis
- B. Addison disease
- C. Pheochromocytoma (Correct Answer)
- D. Conn Syndrome
Explanation: Pheochromocytoma - Pheochromocytoma is a tumor of the adrenal medulla that secretes excessive amounts of catecholamines (epinephrine and norepinephrine). - Vanillylmandelic acid (VMA) is a breakdown product of these catecholamines [1], so its levels are elevated in the urine of patients with pheochromocytoma. Tuberous sclerosis - Tuberous sclerosis is a genetic disorder characterized by the growth of numerous non-cancerous tumors in various organs. - While it can be associated with renal angiomyolipomas or brain lesions, it does not directly cause elevated VMA levels. Addison disease - Addison disease is characterized by adrenal insufficiency [2], meaning the adrenal glands produce insufficient amounts of hormones like cortisol and aldosterone. - This condition is not associated with the overproduction of catecholamines or elevated VMA. Conn Syndrome - Conn syndrome (primary hyperaldosteronism) is due to an overproduction of aldosterone by the adrenal glands, often caused by an adrenal adenoma [3]. - Aldosterone is a mineralocorticoid, and its overproduction does not lead to increased catecholamine metabolism or elevated VMA levels.
Question 2: Best way to localize extra-adrenal pheochromocytoma:
- A. X-ray
- B. Clinical examination
- C. VMA excretion
- D. Nuclear medicine scan (MIBG scan) (Correct Answer)
Explanation: ***Nuclear medicine scan (MIBG scan)*** - **Iodine-131-metaiodobenzylguanidine (MIBG) scan** is the imaging modality of choice for localizing extra-adrenal pheochromocytomas due to its high specificity for **neuroendocrine tumors** like pheochromocytomas and paragangliomas. - MIBG is structurally similar to **norepinephrine** and is actively taken up by adrenergic neurons, allowing visualization of hypersecreting chromaffin cells wherever they are located in the body. *X-ray* - **X-rays** provide limited soft tissue detail and are generally not useful for localizing pheochromocytomas, especially extra-adrenal ones. - They may show calcifications in some tumors but lack the sensitivity and specificity needed for definitive localization. *Clinical examination* - A **clinical examination** can identify signs and symptoms suggestive of pheochromocytoma (e.g., hypertension, palpitations, sweating) but cannot localize the tumor itself. - Localization requires **imaging studies** due to the variable and often deep-seated location of these tumors. *VMA excretion* - **Vanillylmandelic acid (VMA) excretion** is a biochemical test used to diagnose pheochromocytoma by measuring catecholamine metabolites in urine. - While it confirms the presence of a catecholamine-secreting tumor, it provides **no information about the tumor's location**.
Question 3: Which of the following changes in voice is not produced as a result of external laryngeal nerve injury post thyroidectomy?
- A. Inability to sing at higher ranges
- B. Poor volume and projection
- C. Hoarseness (Correct Answer)
- D. Voice fatigue
Explanation: ***Hoarseness*** - **Hoarseness** is primarily caused by injury to the **recurrent laryngeal nerve (RLN)**, which innervates most intrinsic laryngeal muscles responsible for vocal cord adduction and abduction. - An external laryngeal nerve (ELN) injury affects the **cricothyroid muscle**, leading to less tension on the vocal cords, but typically not frank hoarseness. *Voice fatigue* - Injury to the external laryngeal nerve (ELN) weakens the **cricothyroid muscle**, which is responsible for tensing and elongating the vocal cords. - This weakness leads to greater effort required to maintain vocal quality, resulting in **voice fatigue**. *Inability to sing at higher ranges* - The **cricothyroid muscle**, innervated by the ELN, is crucial for increasing vocal cord tension. - Increased tension is necessary for adjusting vocal pitch and reaching **higher frequencies** or notes. *Poor volume and projection* - The cricothyroid muscle's role in vocal cord tension contributes to the efficiency of vocal fold vibration. - Reduced tension due to ELN injury can lead to decreased **vocal power and projection**.
Question 4: Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
- A. I131 (Correct Answer)
- B. 99m Tc
- C. 32p
- D. MIBG
Explanation: ***I131*** - **Radioactive iodine (I131)** is specifically absorbed by **well-differentiated thyroid cancer cells** because these cells retain the ability to uptake iodine, unlike other types of cancer cells. - Used for **ablating residual thyroid tissue** after surgery and for treating **metastatic well-differentiated thyroid carcinoma** [1]. *99m Tc* - **Technetium-99m (99m Tc)** is primarily used for **diagnostic imaging** (e.g., thyroid scans, bone scans), not for therapeutic treatment of thyroid cancer. - It has a short half-life and emits gamma rays, making it suitable for imaging but generally not for delivering sustained radiation for therapeutic effect. *32p* - **Phosphorus-32 (32p)** is a beta-emitting radionuclide used in the treatment of certain hematological malignancies, such as **polycythemia vera**, and for palliative treatment of bone metastases. - It is not selectively taken up by thyroid cancer cells and therefore is not used in the treatment of thyroid carcinoma. *MIBG* - **Metaiodobenzylguanidine (MIBG)**, often labeled with I123 (diagnostic) or I131 (therapeutic), is used in the diagnosis and treatment of **neuroendocrine tumors** like **pheochromocytoma** and **neuroblastoma**. - Its uptake mechanism targets cells of neuroectodermal origin, which is distinct from the iodine uptake mechanism of thyroid cells.
Question 5: Thyroid storm during surgery is due to?
- A. Perioperative intervention
- B. Inadequate preoperative preparation (Correct Answer)
- C. Glucocorticoid side effect
- D. Rough handling during surgery
Explanation: ***Inadequate preoperative preparation*** - **Thyroid storm** is a life-threatening exaggeration of hyperthyroidism, often triggered in patients who are **inadequately prepared** for surgery. - This typically means insufficient control of thyroid hormone levels (e.g., with antithyroid drugs, beta-blockers) prior to a surgical stressor. *Perioperative intervention* - While surgery itself is a stressor, a properly performed **perioperative intervention** on a well-prepared patient is less likely to trigger thyroid storm. - The problem is not the intervention itself, but the patient's underlying uncontrolled hyperthyroid state. *Glucocorticoid side effect* - **Glucocorticoids** are often used to treat thyroid storm, not cause it. - They help reduce peripheral conversion of T4 to T3 and provide adrenal support. *Rough handling during surgery* - While **rough handling** during thyroid surgery (e.g., excessive manipulation of the thyroid gland) can, in theory, release some thyroid hormone, it is a less significant factor in triggering thyroid storm than overall systemic hyperthyroidism. - The primary cause remains **inadequate systemic control** of thyroid hormone levels.
Question 6: In surgical stress all hormones are increased except:
- A. Insulin (Correct Answer)
- B. Epinephrine
- C. ACTH
- D. Cortisol
Explanation: ***Insulin*** - While other **stress hormones** increase, **insulin** levels typically **decrease** or remain stable due to increased **insulin resistance** during surgical stress. - This physiological response aims to maintain **blood glucose** levels for energy during heightened metabolic demands. *Epinephrine* - **Epinephrine** (adrenaline) is a key **catecholamine** released during surgical stress, leading to a "fight or flight" response. - It increases **heart rate**, **blood pressure**, and promotes **gluconeogenesis** to supply quick energy. *ACTH* - **Adrenocorticotropic hormone (ACTH)** is released from the **pituitary gland** in response to surgical stress. - **ACTH** stimulates the adrenal cortex to produce **cortisol**, a critical stress hormone. *Cortisol* - **Cortisol** levels significantly rise during surgical stress, mediated by **ACTH** release. - It plays a crucial role in **modulating inflammation**, **glucose metabolism**, and maintaining **hemodynamic stability**.
Question 7: Which nerve is most likely injured during a thyroidectomy?
- A. Hypoglossal
- B. Phrenic nerve
- C. Superior laryngeal
- D. Recurrent laryngeal (Correct Answer)
Explanation: ***Recurrent laryngeal*** - The **recurrent laryngeal nerves** are highly susceptible to injury during thyroidectomy due to their close anatomical proximity to the **thyroid gland** and their relatively superficial course within the operative field. - Injury to these nerves can lead to **vocal cord paralysis**, resulting in **hoarseness** or, in cases of bilateral injury, severe airway compromise. *Hypoglossal* - The **hypoglossal nerve** (CN XII) innervates the muscles of the tongue and is located more superiorly and medially, well outside the typical dissection planes for a thyroidectomy. - Damage to this nerve would primarily affect **tongue movement** and speech articulation, symptoms not commonly associated with thyroid surgery complications. *Phrenic nerve* - The **phrenic nerve** innervates the diaphragm and is situated deep in the neck and thorax, far from the thyroid surgical field. - Injury during thyroidectomy is extremely rare and would lead to **diaphragmatic paralysis**, causing respiratory difficulties. *Superior laryngeal* - The **superior laryngeal nerve** descends alongside the superior thyroid artery and typically divides into internal and external branches; the **external branch** is at risk during ligation of the superior thyroid pedicle. - While it can be injured, the **recurrent laryngeal nerve** is more frequently and severely affected, particularly its motor function to the intrinsic laryngeal muscles, which is most critical for voice production.
Question 8: Most sensitive investigation for preoperative localization of abnormal parathyroid glands is
- A. Neck ultrasound
- B. (99mTc) labelled Sestamibi isotope scan (Correct Answer)
- C. CT scan
- D. MRI
Explanation: ***(99mTc) labelled Sestamibi isotope scan*** - This scan uses a **radioactive tracer** that is preferentially taken up and retained by hyperfunctioning parathyroid tissue, making it highly sensitive for identifying **abnormal parathyroid glands**, especially parathyroid adenomas. - It is particularly useful for detecting **ectopic parathyroid glands** and in cases of persistent or recurrent hyperparathyroidism. *Neck ultrasound* - While useful for localizing parathyroid glands, its sensitivity can be limited by **operator dependence**, gland size, and location (e.g., retrosternal). - It is generally good for initial screening but not as sensitive as Sestamibi for identifying all abnormal glands, especially those located in challenging areas. *CT scan* - CT scans can visualize larger parathyroid adenomas, but their sensitivity is lower than Sestamibi scans for smaller lesions or those with **atypical locations**. - It is often used as a **second-line imaging modality** when Sestamibi is inconclusive or to complement findings. *MRI* - MRI can provide detailed anatomical information and identify parathyroid glands, but its sensitivity for detecting abnormal parathyroid tissue is generally **comparable to or slightly less** than CT and inferior to Sestamibi scanning. - It may be considered in cases of unclear findings from other modalities or when radiation exposure is a concern.
Question 9: Hypoparathyroidism following thyroid surgery occurs within:
- A. 2 - 5 days
- B. 7-14 days
- C. 24 hours (Correct Answer)
- D. 2 - 3 weeks
Explanation: ***24 hours*** - **Symptomatic hypocalcemia** from hypoparathyroidism typically **begins within 24 hours** and peaks at **24-48 hours** post-thyroidectomy. - Serum calcium levels start to decline within the **first 24 hours** as parathyroid hormone (PTH) production decreases due to surgical trauma, ischemia, or inadvertent removal/damage to parathyroid glands. - Most patients who develop clinically significant hypoparathyroidism show **early signs** including perioral numbness, paresthesias, and positive Chvostek's or Trousseau's signs within this timeframe. - **Early monitoring** of calcium levels (usually at 6-12 hours postoperatively) is standard practice to detect and treat hypocalcemia promptly. *2 - 5 days* - While some cases may continue to worsen during this period, the **onset** typically occurs much earlier (within 24-48 hours). - This timeframe represents continuation or persistence of hypocalcemia rather than initial manifestation. - Waiting 2-5 days to detect hypoparathyroidism would be considered delayed diagnosis in modern practice. *7-14 days* - This timeframe is **too late** for acute postoperative hypoparathyroidism diagnosis. - By this time, the focus shifts to determining whether hypoparathyroidism is **transient** (resolving within 6 months) or **permanent**. - Most acute symptomatic cases have already been identified and are under treatment by this period. *2 - 3 weeks* - Hypoparathyroidism presenting at **2-3 weeks** would be highly unusual for post-thyroidectomy complications. - At this stage, clinicians are assessing for **recovery of parathyroid function** rather than initial onset. - **Permanent hypoparathyroidism** is only diagnosed if hypocalcemia persists beyond **6 months**, not at 2-3 weeks.
Question 10: A patient diagnosed with papillary carcinoma of the thyroid underwent a whole-body iodine scan six weeks after surgery, which revealed residual disease. The next best step is:
- A. Surgical removal of residual disease
- B. Radioiodine ablation (Correct Answer)
- C. FNAC of the residual tissue followed by radioiodine ablation
- D. Neck ultrasound and serum thyroglobulin level measurement
Explanation: ***Radioiodine ablation*** - **Radioiodine (RAI) ablation** is the standard treatment for residual thyroid cancer after surgery, especially for **papillary thyroid carcinoma**, which typically avidly takes up iodine. - The goal is to destroy any remaining microscopic thyroid cells or cancer cells that may not have been removed surgically. - This is the **next best step** when residual disease is detected on whole-body iodine scan. *Surgical removal of residual disease* - While surgical removal is a primary treatment, attempting another surgery for **microscopic residual disease** detected by a whole-body scan might be difficult and carry higher risks. - RAI ablation is generally preferred for **diffuse residual disease** or microscopic foci that are not amenable to surgical resection. *FNAC of the residual tissue followed by radioiodine ablation* - **Fine needle aspiration cytology (FNAC)** typically targets discrete nodules, and the whole-body scan indicates diffuse or multifocal residual tissue, making FNAC less practical. - Since the diagnosis of **papillary carcinoma** is already established histologically, re-biopsy of residual tissue is unnecessary before RAI ablation, especially if the residual disease is diffuse. - This would cause unnecessary delay in definitive treatment. *Neck ultrasound and serum thyroglobulin level measurement* - These are **diagnostic and monitoring tools**, not definitive treatments for established residual disease. - While crucial for initial evaluation and ongoing surveillance, they do not eliminate the residual cancer, which is the immediate priority.
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