Overview
Definition:
Ectopic intrathymic parathyroid refers to the presence of parathyroid tissue within the thymus gland, a rare anatomical anomaly
These glands are typically supernumerary and can contribute to or cause hyperparathyroidism
Their location in the mediastinum poses surgical challenges compared to more common ectopia sites.
Epidemiology:
Ectopic parathyroid glands account for approximately 2-5% of all parathyroid adenomas or hyperplastic glands
Intrathymic location is among the rarer forms of ectopia
Incidence is not precisely known due to asymptomatic nature until functional abnormality occurs
Affects all age groups, more common in adults.
Clinical Significance:
Intrathymic ectopic parathyroids are clinically significant when they become hyperfunctional, leading to primary hyperparathyroidism
Diagnosis can be challenging, often requiring advanced imaging and a high index of suspicion
Surgical removal is curative, but the mediastinal location necessitates specific surgical techniques, often minimally invasive approaches like VATS, to ensure complete excision and minimize morbidity.
Diagnostic Approach
History Taking:
Detailed history of symptoms suggestive of hypercalcemia: fatigue, bone pain, nephrolithiasis, constipation, cognitive dysfunction, pancreatitis, peptic ulcers
Previous thyroid or parathyroid surgery
Family history of endocrine disorders (MEN syndromes)
Red flags include persistent hypercalcemia despite presumed complete parathyroidectomy.
Physical Examination:
General examination for signs of hypercalcemia (e.g., dehydration)
Palpation of the neck for any palpable masses or lymphadenopathy, though intrathymic glands are deep
Assessment for signs of bone disease or renal calculi.
Investigations:
Serum calcium and parathyroid hormone (PTH) levels are crucial
Elevated calcium and PTH confirm hyperparathyroidism
Renally adjusted calcium
Vitamin D levels
Phosphate
Magnesium
Renal function tests
Imaging: Neck ultrasound is primary for visible glands but may miss intrathymic ones
Sestamibi scanning (99mTc-MIBI) is vital for localizing ectopic glands in the neck and mediastinum
CT scan or MRI of the neck and chest with contrast can further delineate the mass and its relationship to mediastinal structures
4D-CT can offer higher resolution for small lesions
Arterial calcium venous sampling (ACVS) may be used for localization if standard imaging is inconclusive, though less common for mediastinal lesions.
Differential Diagnosis:
Other mediastinal masses (thymoma, teratoma, lymphoma, germ cell tumors)
Metastatic disease
Parathyroid carcinoma (rare)
Tertiary hyperparathyroidism
Familial hypocalciuric hypercalcemia (FHH)
Vitamin D toxicity
Drugs (e.g., thiazides, lithium).
Surgical Management
Indications:
Symptomatic primary hyperparathyroidism confirmed by biochemical tests (elevated serum calcium and PTH)
Asymptomatic hyperparathyroidism with specific criteria met (e.g., serum calcium >1 mg/dL above normal, reduced bone mineral density, renal calculi, age <40 years)
Localization of the ectopic gland confirmed by imaging.
Preoperative Preparation:
Nutritional optimization
Correction of hypercalcemia if severe (hydration, loop diuretics if necessary, bisphosphonates)
Review of imaging studies to meticulously plan surgical approach and identify vascularity
Preoperative antibiotics
Informed consent detailing risks of VATS, anesthesia, and potential complications.
Procedure Steps Vats:
The patient is placed in the lateral decubitus position
A minimal number of ports (usually 2-3) are inserted into the hemithorax
Carbon dioxide insufflation may be used for better visualization
The thymus is dissected to expose the anterior mediastinum
The ectopic parathyroid gland is identified, carefully dissected from surrounding thymic tissue and mediastinal fat, paying close attention to vascular pedicles supplying the gland and avoiding injury to the recurrent laryngeal nerves
The gland is then retrieved through one of the port sites, often placed in a retrieval bag to prevent seeding or loss
Confirmation of gland removal by intraoperative PTH assay may be performed.
Surgical Techniques:
Video-assisted thoracoscopic surgery (VATS) is the preferred minimally invasive approach for intrathymic parathyroid glands due to its ability to provide excellent visualization of the mediastinum and allow for precise dissection
Robotic-assisted thoracic surgery (RATS) is an alternative offering enhanced dexterity
Open thoracotomy is reserved for cases where minimally invasive approaches are not feasible or if complications arise during VATS.
Postoperative Care
Monitoring:
Close monitoring of serum calcium levels postoperatively, typically every 4-6 hours initially, then daily
Watch for hypocalcemia, which can occur due to the sudden drop in PTH
Monitor vital signs and fluid balance
Pain management
Respiratory monitoring.
Management Of Hypocalcemia:
Symptomatic hypocalcemia (tingling, tetany, laryngospasm) requires immediate intravenous calcium gluconate
Asymptomatic hypocalcemia is managed with oral calcium and calcitriol
The goal is to gradually wean off supplementation as residual parathyroid function returns or if remaining glands compensate.
Dietary Considerations:
Gradual reintroduction of oral intake
Calcium and vitamin D supplementation as prescribed, tailored to serum calcium levels
Avoidance of foods high in phosphate if renal function is compromised.
Discharge Planning:
Patient education on signs of hypocalcemia and when to seek medical attention
Prescription for oral calcium and calcitriol
Follow-up appointments with endocrinology and surgery
Instructions on wound care and activity restrictions.
Complications
Early Complications:
Bleeding or hematoma formation in the mediastinum
Recurrent laryngeal nerve injury (hoarseness, vocal cord paralysis)
Pneumothorax
Infection
Persistent or recurrent hypercalcemia if gland not completely removed or if other ectopic glands exist
Hypocalcemia (most common and expected).
Late Complications:
Long-term hypocalcemia requiring ongoing supplementation
Scarring and adhesions in the thoracic cavity
Recurrence of hyperparathyroidism if residual parathyroid tissue remains or if hyperplastic instead of adenomatous
Adhesion formation leading to chest pain.
Prevention Strategies:
Meticulous surgical technique with clear visualization of the gland and its vascular supply
Use of intraoperative PTH monitoring to confirm complete gland removal
Careful dissection to avoid injury to adjacent structures
Adequate preoperative imaging to identify all ectopic glands
Appropriate management of hypocalcemia postoperatively.
Prognosis
Factors Affecting Prognosis:
Successful complete removal of the hyperfunctional ectopic gland is the primary determinant of good prognosis
The presence of other ectopic glands or multiglandular disease (MEN syndromes) can affect long-term outcomes
The severity of preoperative hypercalcemia and its impact on bone and renal health can also influence recovery.
Outcomes:
The prognosis for patients with ectopic intrathymic parathyroid glands removed via VATS is generally excellent, with biochemical cure rates exceeding 95% for single adenomas
Symptoms of hyperparathyroidism typically resolve within weeks to months after successful surgery
Long-term calcium homeostasis is usually restored.
Follow Up:
Regular follow-up with endocrinology is recommended, including periodic checks of serum calcium and PTH levels
The frequency of follow-up depends on the cause of hyperparathyroidism and any associated conditions
Imaging may be repeated if recurrence is suspected
Patients with a history of MEN syndrome require lifelong surveillance for other endocrine tumors.
Key Points
Exam Focus:
Localization of ectopic glands is paramount, with sestamibi scan being the gold standard
VATS is the preferred minimally invasive approach for intrathymic glands
Postoperative hypocalcemia is common and requires careful management
Differentiate between adenoma, hyperplasia, and carcinoma
Consider MEN syndromes in familial cases.
Clinical Pearls:
Always suspect ectopic parathyroid glands in cases of persistent hyperparathyroidism after neck exploration or with absent glands on neck imaging
Intraoperative PTH monitoring is invaluable for confirming complete resection, especially in challenging locations
Thorough mediastinal exploration is crucial during VATS.
Common Mistakes:
Incomplete surgical resection due to difficulty in localization or identification of all abnormal glands
Overlooking the possibility of mediastinal or intrathymic ectopia
Aggressive dissection leading to recurrent laryngeal nerve injury
Inadequate management of postoperative hypocalcemia, leading to significant morbidity
Failure to investigate for MEN syndromes in appropriate patients.