Teratoma, a common type of germ cell tumor, most often occurs in the gonads. About 15% of the patients have extragonadal teratoma (e.g., the sacrococcygeal region, retroperitoneum, mediastinum, and pineal region), while this tumor rarely occurs in the head and neck is rare (3% to 5%)(2, 3). Teratoma of the parotid gland is extremely rare and seldom reported. After reviewing relevant literature, only 9 patients with parotid gland teratoma were reported from 1975 to 2019 worldwide (Table 1)(1, 4-11). We failed to access the 2nd and 6th patients' detailed information even though we made substantial effort to do so. Finally, only 8 patients with teratoma of the parotid gland and the relatively complete information (including the one in this report) were analyzed and summarized.
Teratoma most often occurs in females, according to relevant literature(12). About 90% of the head's teratoma occurred in infancy or childhood(13), and a few developed in adulthood. In the older population, teratoma can easily transform into a malignant tumor(14). Among the above-mentioned 8 patients with teratoma in the parotid gland, 6 were females (75.0%), and 2 were males (25.0%), at a ratio of 3:1. Their age ranged from 9 to 36 years, with an average of 22.3 years. The patient in this report was a 36-year-old man, who was the oldest among all patients diagnosed with teratoma in the parotid gland so far. All patients had the teratoma involving unilateral parotid gland, with 4 on the left side (50.0%) and 4 on the right side (50.0%). The patient in this report had the lesion in the deep lobe that extended into the parapharyngeal space, while in other reported cases, the lesions involved the superficial lobe (including 1 case involving a deep lobe). The maximum diameter of the lesion ranged from 1.0 to 3.2cm. All patients visited the hospital for a painless tumor. The course of the disease was between 2 weeks and 4 years, averaging 11 months. Patients had no symptoms (e.g., limitation of mouth opening, hearing impairment, or facial nerve palsy).
Teratoma is a tumor derived from germ cells that can potentially differentiate into somatic cells. According to Batsakis et al(15), most teratomas contain the elements of all ectoderm, mesoderm, and entoderm and can differentiate into skin, nerve, bone, and fatty tissues. In addition, most tumors are cystic (containing liquid, sebum debris, hair, and fatty ingredients) or solid (containing more complex ingredients) and can contain mature, immature, or both mature and immature elements, which distinguishes them from epidermoid cysts and dermoid cysts. Most benign teratomas are cystic, also known as mature cystic teratomas. Ohta et al(9) stated that a teratoma containing skin appendages and cartilage tissues in the cyst wall could be diagnosed as a mature cystic teratoma. Under a microscope, the lesion's cyst wall in this report was lined with layered squamous epithelium, containing sebaceous gland cells, and hyaline cartilage, while fatty tissues were well-differentiated, meeting the diagnostic standards of a mature cystic teratoma.
With reference to clinical physical examination, preoperative diagnostic methods for teratoma in the parotid gland include imaging examinations, such as ultrasonography, CT, and MRI. Ultrasonography is convenient and easy to perform. Under ultrasonography, typical teratoma usually appears as heterogeneous strong light masses and solid-cystic masses containing multiple ingredients and with uneven echo. However, this approach may not be useful for teratoma located deeper within the tissue, which usually requires a CT and MRI scan. Calcification (or ossification) and fatty elements in a teratoma can be visualized on the CT, and a fat-liquid level, hair, tooth, or fat-liquid complex can lead to a definite teratoma diagnosis(16). MRI allows better observation of soft tissues, as well as histopathological changes, such as intratumoral mucus, cartilage matrix, fat, and calcification. It can also be specifically used for fat signaling as fat contains a large number of hydrogen protons and is shown as a high signal in both T1W1 and T2W1, and presented as a low signal due to inhibition of the high signal in the fat-suppressed MRI sequence(17), which increases tissue contrast and reduces artifacts and is of great significance in identifying a teratoma. The combined use of CT and MRI allows qualitative diagnosis and clear observation of the lesion location and scope and its relationship with adjacent tissues. Imaging results of our patient suggested calcification, fat, keratinized substances in the lesion, and the typical fat-liquid levels. Teratoma in the parotid gland with atypical imaging findings can be distinguished from a lipoma, dermoid cyst, epidermoid cyst, branchial cleft cyst, vascular tumor, and pleomorphic adenoma. In this report, the tumor extended to the parapharyngeal space, and the lesion was of a gourd-like shape, which has been detected as two separate lesions on CT and MRI images. Yet, during surgery, it was revealed to be a single lesion that was soft, limited, and surrounded by adjacent structures (the ascending ramus of the mandible, mastoid tip, and peripheral vessels and nerves), thus seeming more like two separate lesions.
The therapy for teratoma in the parotid gland is the same as that used for lipoma and other benign tumors located in the parotid gland, i.e., partial or total lobotomy of the parotid gland by preserving the facial nerve. The part of the parotid gland that needs to be removed is determined according to the tumor's location and size (10, 18). Studies on postoperative complications are rare. Generally, it is believed that such complications result from parotid gland removal and are irrelevant to the nature of the tumor. Postoperative transient facial nerve weakness is the most common complication among patients. Postoperative recurrence of teratoma in the parotid gland is extremely rare. According to existing literature, one patient showed in situ recurrences after surgery(7). Incomplete resection of the tumor may be a possible cause of recurrence, which should be noted in clinical practice. The patient in this report was young, so the superficial lobe in his parotid gland was retained after complete tumor resection, partial parotid gland excision, and anatomical facial nerve relaxation. After surgery, the patient developed a mild facial nerve symptom (he was not able to completely close his left eyelid); this symptom was relieved 4 months later. He had no signs of recurrence of the teratoma during the 15-month follow-up and is still being followed up.
To sum up, teratoma in the parotid gland is rare. A fatty tumor in the parotid gland may suggest the presence of parotid gland teratoma. Preoperative CT and MRI imaging findings may help localize and perform differential diagnosis of teratoma in the parotid gland by showing calcification, fatty elements, and a fat-liquid level in the parotid gland cyst. Yet, the final diagnosis must be confirmed by histopathological examination. For teratoma in the parotid gland, surgical resection is the preferred and effective therapy, in which the facial nerve function should be protected. Patients with teratoma in the parotid gland have a good prognosis but should be regularly followed up.