Post–Auricular Teratoma Masquerading as a Branchial Cleft Cyst

Significance Statement

Post–auricular teratomas are exceptionally rare in pediatric patients and can pose a diagnostic challenge due to their variable imaging characteristics. These lesions may mimic other congenital cystic masses, leading to potential misdiagnosis. Imaging modalities played a crucial role in diagnosis and surgical planning.

An 8 month-old boy was referred to our center with a palpable mass behind the left ear. There was no history of trauma in the patient who was born at term with spontaneous vaginal delivery. Physical examination revealed a mobile, painless, and non–discolored lesion measuring approximately 1 cm in diameter in the left post–auricular area. No lymphadenopathy was observed in the neck region. Ultrasonography (USG) revealed a smoothly circumscribed, heterogeneous hypoechoic lesion in the subcutaneous tissue with no blood supply on Doppler imaging. Non-contrast computed tomography (CT) imaging revealed no calcification in the hypodense lesion, which had a mean density of 16 hounsfield units (HU, Figure 1a). Contrast-enhanced magnetic resonance imaging (MRI) showed the lesion to be hypointense on T1-weighted images and slightly hyperintense on T2-weighted images. Peripheral linear contrast enhancement was present in the lesion, and there was no evidence of diffusion restriction (Figure 2). The patient was diagnosed with a complicated brachial cleft cyst and recommended for surgery; however, this was declined and the patient presented again 3 years later due to the enlargement of the lesion. A subsequent non-contrast CT scan revealed a lesion with heterogeneous dense characteristics and areas of fat density (mean −22 HU, Figure 1b). MR imaging showed that the lesion had increased in size posteriorly and measured approximately 26 × 26 × 16 mm. In addition to the cystic area detected in the previous examination, there was a solid component, hypointense on T1-weighted image, hyperintense on T2-weighted image, showing marked contrast enhancement (Figure 3). There was no demarcation between the lesion and the parotid gland anteriorly. The patient was operated with a preliminary diagnosis of teratoma based on the imaging features. Histopathological examination revealed a diagnosis of mature cystic teratoma. Postoperative complications included the development of facial paralysis, and no recurrence was observed during the subsequent 2 years.

Figure 1.

The first non-contrast CT axial section (a) shows a hypodense lesion (asterix) in the left postauricular area with a mean density of 16 HU. Three years later, the non-contrast CT scan (b) shows that the lesion (asterisk) has a mean density of −22 HU and is enlarged posteriorly (arrow).

Figure 2.

Magnetic resonance imaging reveals the presence of a cystic lesion (see arrows) in the left post–auricular area. This lesion exhibits distinct characteristics on various MRI sequences, including hypointense signal on T1-weighted axial images (a), hyperintense signal on T2-weighted axial images (b), and perifocal contrast enhancement on postcontrast T1-weighted axial images (c).

Figure 3.

Three years later, magnetic resonance imaging of the patient showed a newly-developed solid component (red arrows) that was hypointense on T1-weighted axial section (a), hyperintense on T2-weighted axial section (b), and prominently contrasted on postcontrast section (c). On the T2-weighted section, the signal intensity of the previous cystic component has changed (white arrow).

The postauricular region is the least common site in the head and neck region where teratoma is rarely observed in children.^1,2 These tumors are often diagnosed in the first few years of life, with the majority being benign, slow-growing masses. The most common presenting symptom is a painless, soft mass located behind the ear, though some patients may experience associated symptoms such as hearing loss, facial asymmetry, or ear discharge, depending on the tumor’s size and location.

In the case of teratomas, prenatal and postnatal period imaging plays a pivotal role in diagnosis. The majority of cases are diagnosed through antenatal USG. Ultrasonography is frequently the first modality; however, to gain a better understanding of the tumor’s internal components and extent, further imaging with CT or MRI is often required. On CT scans, mature teratomas typically demonstrate mixed-density masses, with areas of fat attenuation, calcifications, and soft tissue components. MRI is considered the gold standard for evaluation, offering superior soft tissue contrast. The MRI is the most effective tool for preoperative evaluation of tumor invasion. On MRI, the appearance of the tumor is that of a single or multiloculated, well circumscribed, solid and/or cystic heterogeneous mass that may contain fat and calcification.^3-5

In the present case, the absence of fatty tissue, calcification, or a solid component in an uniloculated cystic lesion at the time of initial presentation suggested a branchial cleft cyst. However, the literature contains rare cases of purely cystic mature cystic teratomas. ³