ectopic thymus

Ectopic Thymus: A Rare Condition

Ectopic thymus, also known as ectopic cervical thymus, is a rare condition where thymus tissue is found in an abnormal location outside the anterior mediastinum. This can occur due to either a failure of descent or a failure of involution of normal thymus tissue during embryonic development.

Characteristics

• Ectopic thymus tissue is usually found in the neck, but can also be located near the thyroid gland or salivary glands.
• It may cause a mass in the neck that can compress the trachea and esophagus.
• The condition is often diagnosed with radiology techniques such as ultrasound or magnetic resonance imaging (MRI).

Prevalence

• Ectopic cervical thymus is an exceedingly rare condition, representing less than 1% of all cervical lesions in children.
• It is more commonly found in mice and rats, but has been reported in humans.

Symptoms

• In most cases, ectopic thymus does not cause symptoms.
• However, when it occurs in the neck, it can lead to compression of the trachea and esophagus, which may result in respiratory or swallowing difficulties.

Diagnosis

• Ectopic thymus is typically diagnosed with radiology techniques such as ultrasound or MRI.
• Familiarity with embryonic development, anatomy, and dynamic physiology of the thymus is essential to avoid unnecessary imaging or invasive procedures.

References

• [1] Ectopic cervical thymus can be found in up to 90% of some lines of mice in various cervical locations. (Source: Search result 2)
• [2-5] Ectopic thymus is a rare condition where thymus tissue is found in an abnormal location, potentially causing a mass in the neck that can compress the trachea and esophagus. (Sources: Search results 4, 10, 11, 13)
• [6-8] Ectopic cervical thymus is an uncommon cause of a neck mass in an infant and occurs in the pathway of normal descent of the thymus from the angle of the mandible to the anterior mediastinum. (Sources: Search results 15, 12, 13)
• [9-10] Ectopic thymus may mimic malignant thyroid nodules with microcalcifications, but can be distinguished by the lack of associated acoustic shadowing from the hyper-echoic foci in ectopic thymic tissue. (Sources: Search results 14, 10)

Ectopic thymus, also known as an abnormal location of thymic tissue, can present with various signs and symptoms, although it is often asymptomatic.

Common presentations:

• A firm, asymptomatic neck mass [4]
• Compressive symptoms in some cases, including:
  • Dyspnea (difficulty breathing) [7]
  • Hoarseness
  • Stridor (a high-pitched sound while inhaling)
  • Dysphagia (difficulty swallowing)
  • Pain in the neck or throat area [6]
• Transient swelling above the suprasternal notch during straining, crying, or other activities that increase intrathoracic pressure [5]

Rare presentations:

• Feeding difficulties
• Breathing difficulties
• Horner’s syndrome (a rare condition affecting the nerves controlling facial expressions and eye movements) in rare cases [4, 5]

It's essential to note that ectopic thymus is often diagnosed incidentally during radiological investigations for other reasons. If you suspect an ectopic thymus, it's crucial to consult a medical professional for proper evaluation and treatment.

References:

[1] Ectopic thymic tissue generally presents as a firm, asymptomatic neck mass [4] [2] Compressive symptoms may occur in some cases, presenting with feeding difficulties, breathing difficulties, or Horner’s syndrome in rare cases [4, 5] [3] Transient swelling above the suprasternal notch appears when an increase in intrathoracic pressure occurs, such as during straining, crying or, as in our case, during a Valsalva maneuver [5] [4] Ectopic thymus is usually asymptomatic; however, compressive symptoms may occur in some cases, presenting with feeding difficulties, breathing difficulties, or Horner’s syndrome in rare cases [4, 5] [5] A transient swelling above the suprasternal notch appears when an increase in intrathoracic pressure occurs, such as during straining, crying or, as in our case, during a Valsalva maneuver [5] [6] Neck pain may also occur due to cyst growth. In our case, the patient experienced neck pain and was diagnosed with ectopic thymus [6] [7] Dyspnea (difficulty breathing) is one of the compressive symptoms that can occur in some cases [7]

Diagnostic Tests for Ectopic Thymus

Ectopic thymus, a rare condition where thymus tissue is found in an abnormal location, can be challenging to diagnose. However, various diagnostic tests can help confirm the presence of this condition.

• Radiology: Imaging studies such as ultrasound, magnetic resonance imaging (MRI), and computer tomography (CT) scans are commonly used to diagnose ectopic thymus. These tests can help identify the mass in the neck and determine its location and size [12][7].
• Biopsy: A biopsy, which involves taking a sample of tissue from the affected area, is often necessary to confirm the diagnosis of ectopic thymus. The biopsy sample is then examined under a microscope to determine the presence of thymic tissue [5][9].
• Contrast-enhanced CT scan: This test can provide detailed images of the mass and its relationship with surrounding structures, such as blood vessels and nerves [8].

It's worth noting that diagnosis can be made through radiology like ultrasound or MRI, with surgery being an option for removal if necessary. Recurrence post-surgery is rare [6].

Ectopic Thymus Differential Diagnosis

The differential diagnosis of an ectopic thymus, a rare condition where the thymus gland is located outside its normal position in the chest, can be extensive and varied. Here are some possible conditions that may be considered in the differential diagnosis:

• Thyroglossal duct cysts: These are congenital anomalies that can mimic an ectopic thymus [1].
• Dermoid cysts: These are benign tumors that can contain skin, hair, and other tissues, and may be confused with an ectopic thymus [1].
• Thyroid nodules: Although less common in children than adults, thyroid nodules can be a consideration in the differential diagnosis of an ectopic thymus [3].
• Branchial cleft anomalies: These are congenital defects that can occur along the branchial clefts and may be confused with an ectopic thymus [9].
• Lymphadenopathy: This is a condition characterized by the enlargement of lymph nodes, which can be a consideration in the differential diagnosis of an ectopic thymus [9].

It's worth noting that an ectopic thymus is often misdiagnosed as a thyroglossal duct cyst, branchial remnant, cyst, or neoplasia [6]. A precise differential diagnosis requires careful evaluation and imaging studies such as ultrasound or MRI.

References:

[1] Alnosair AA (2022) - The differential diagnosis of a cervical mass in children includes congenital or acquired neck lumps such as thyroglossal duct cysts, dermoid ...

[3] Karavas E (2021) - In the differential diagnosis, it is mostly confused with thyroid nodules. Although thyroid nodules are less common in children than adults, ...

[6] Goodman EM (2024) - Ectopic cervical thymus is an uncommon cause of a neck mass and is often misdiagnosed as a thyroglossal duct cyst, branchial remnant, cyst, or neoplasia.

[9] Stasiak M (2019) - In addition, the lesion margins may be irregular. Such features suggest PTC and require precise differential diagnosis. The extra-thyroid ...