Rarely normal thyroid tissue may occur within the lung. This is often asymptomatic but can be misdiagnosed as a primary or metastatic tumor on imaging studies.
Frequency: very rare (1 in 100,000)
Risk factors:
(1) female gender
(2) Asian
(3) thyroid disease
The patient may be worked up for:
(1) assessment of a lung nodule
(2) assessment of possible metastasis from a thyroid carcinoma
(3) assessment of possible metastasis from other tumor
(4) source of a malignant thyroid carcinoma
(5) symptoms caused by the ectopic tissue (most patients are asymptomatic)
Features:
(1) A biopsy of the lesion shows normal thyroid tissue.
(2) Location in a upper lobe.
(3) Visible on a thyroid scan with I-131.
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