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Neuroradiology Case of the Week

Case 299

Justin Brucker, CC4, Virendra Kumar, MD, and Sudhir Kathuria, MD

Clinical Presentation: A 27-year-old female, with a history of hypothyroidism and suicide attempts, tried to hang herself. CT of the neck was obtained to evaluate for soft tissue and cervical spine injury.

Imaging Findings: No appreciable soft tissue injury or cervical bone fracture is seen.
Incidentally, there is a lobulated soft tissue mass at the base of the tongue with attenuation similar to that of the neck vessels (Fig. 1). The thyroid gland is absent from its usual location (Fig. 2).

Diagnosis: Lingual (ectopic) thyroid gland

Discussion: The thyroid gland usually sits anterior or lateral to the trachea, between the second and fourth cartilage rings. In rare events (1 in 100,000-300,000 people), thyroid tissue may be present elsewhere in the body; a so-called "ectopic thyroid" [1-3].  There is a female:male ratio of 4-7:1 for ectopic thyroid [2]. Ninety percent of the time it is a "lingual thyroid" [1,4], which is found in the base of the tongue at the foramen cecum. It represents the thyroid's failed descent of its anlage between the 3rd and 7th week of development. Anomalous migration may account for the appearance of the thyroid anywhere in the midline neck, between the tongue and the anterior mediastinum [1-4]. Esophageal, intratracheal, intra-aortic, intracardiac, and intra-abdominal cases have also been reported [1-3]. The specific developmental insult is unknown, but it may have to do with maternal anti-thyroid antibodies impairing normal thyroid cell migration [2].
     A lingual thyroid often presents as a smooth oropharyngeal mass that enlarges during puberty, pregnancy, or menstruation [1,2,5]. There may be prominent venous circulation [1], but bleeding is rare [2]. Primary hypothyroidism, with a resultant goiter, may contribute to the mass effect, leading to dysphagia, dysphonea, or dyspnea [1-3]. Thyroid disease is an important clinical feature, since the incidence of ectopic thyroid increases to 1 in 4000-8000 in these patients [1,3]. Furthermore, ectopic thyroid is associated with 24-60% of congenital hypothyroidism cases [3]. However, most patients are clinically euthyroid [3,4].
     Lingual thyroid should be differentiated from a thyroglossal duct cyst, which is a common remnant of thyroid development. Occasionally, a thyroglossal duct cyst may become infected, and can present as an inflamed mass of thyroid and associated lymphoid tissue. An ectopic thyroid runs the risk of being misdiagnosed as such a lesion, and may be erroneously removed, resulting in a profound hypothyroidism [1].
     In addition to clinical exam and lab tests, radionuclide scans, ultrasound, and CT may all be useful in diagnosing an ectopic thyroid, although the latter may be unnecessary [1,2]. For the first test, technetium-99m pertechnetate or iodine-131 can help determine the location and dimensions of the thyroid, although iodine-131 is less often used due to the higher radiation dose [1]. A nuclear scan is also useful in identifying a goiter, although it is not necessarily ruled out by a negative result [4]. It can also help to rule out a thyroglossal duct cyst, lipoma, lymph node, epidermoid cyst, vascular malformation, and malignancy [3]. Ultrasound is less sensitive and specific, but may detect the presence of a normal thyroid (hyperechoic to muscle), thereby eliminating clinical suspicion for an ectopic thyroid, but there runs a risk of mistaking complex muscle architecture for a normal gland [1]. Thirty percent of the time, ectopic thyroid will be found in more than one location [3]. MRI findings for lingual thyroids are comparable to normal thyroid tissue: well-defined masses that on T1, isointense to hyperintense compared to muscle; low to intermediate signal with some cystic features on T2; and mild enhancement [5,6]. Due to its high iodine content and metabolic activity, the thyroid will appear dense on CT with strong enhancement [6]. Still, thyroid scintigraphy remains the study of choice.
     An asymptomatic lingual thyroid, which is most common [3], does not require treatment. In cases of hypothyroidism with glandular enlargement, hormone replacement therapy (HRT) can help minimize the endocrinologic and obstructive symptoms. If obstruction persists or malignancy is suspected (very rare), surgical resection with lifelong HRT may be needed [1,3]. Another option is autotransplantation of the ectopic thyroid to the lateral pharyngeal wall [1].

References:

1. Mussak EN, Kacker A. Surgical and medical management of midline ectopic thyroid. Otolaryngol Head Neck Surg. 2007 Jun;136(6):870-2. [Medline]
2. Tincani AJ, Martins AS, Del Negro A, Araújo PP, Barretto G. Lingual thyroid causing dysphonia: evaluation and management. Case report. Sao Paulo Med J. 2004 Mar 4;122(2):67-9. [Medline]
3. Chawla M, Kumar R, Malhotra A. Dual ectopic thyroid: case series and review of the literature. Clin Nucl Med. 2007 Jan;32(1):1-5. [Medline]
4. Gamblin TC, Jennings GR, Christie DB 3rd, Thompson WM Jr, Dalton ML. Ectopic thyroid. Ann Thorac Surg. 2003 Jun;75(6):1952-3. [Medline]
5. Takashima S, Ueda M, Shibata A, Takayama F, Momose M, Yamashita K. MR imaging of the lingual thyroid. Comparison to other submucosal lesions. Acta Radiol. 2001 Jul;42(4):376-82. [Medline]
6. Mafee MF. Valvassori's Imaging of the Head and Neck, 2nd ed. Thieme. New York. 2005: 719, 783-784.