Mature teratomas occur in various sites and organs, including the ovaries, testes, retroperitoneal region, entire mediastinum, anterior sacral region, and coccygeal region [3].

In addition to this case, five other cases of mature teratomas extending from the anterior mediastinum to the neck have been reported [4,5,6,7,8] (Table 1). The age range is 19–29 years, with an average age of 23 years and the gender ratio was equal with 2 male and 3 female participants.

Surgical removal was challenging due to inflammatory adhesions, necessitating thyroid lobe resection in our case. Due to the lack of histopathological diagnosis and the determination that surgery conducted after the acute phase of inflammation had subsided would be safer than emergency surgery, we opted against performing an urgent operation. Ultimately, opting for a semi-urgent surgical intervention based on imaging findings may have inadvertently facilitated the progression of adhesions over time. These findings underscore the importance of clinical vigilance, as teratomas are often silent manifestations. Surgical complexity underscores the need for meticulous preoperative planning and adaptability to unexpected complications. This series provides valuable insights into managing mature teratomas in atypical locations and encourages further collaborative research for refined strategies. The surgical intervention was initially commenced employing a robot-assisted modality, with the intention of circumventing the necessity for a midline sternotomy, taking into consideration the patient's youthful age and gender. Regrettably, this strategy ultimately led to the need for median sternotomy, resulting in an increase in surgical wound dimensions and prolonged procedural duration. We consider this to be a point for reflection in this case.

The extension pattern of mature teratomas from neck to anterior mediastinum entails two plausible scenarios. There is still no established consensus on the pattern of progression. Yamaguchi et al. proposed anatomically that the tumor advances into the neck because it is enclosed anteriorly by the sternum, posteriorly by the heart, left side by the aorta, with the solid part of the tumor located on the right side of the mediastinum, causing thickening of the right-side wall. While literature reports cases of teratomas extending from neck to anterior mediastinum [9], our case presents a unique pathology. Pathological analysis revealed teratoma components exclusively in the anterior mediastinal tumor, with the neck lesion primarily displaying inflammatory changes. Thus, we propose an extension from anterior mediastinum to neck.

Furthermore, 40–60% of mediastinal teratomas include pancreatic tissue [10, 11], and it is believed that both Langerhans cells and exocrine glands in the pancreatic tissue contribute to cyst formation and inflammatory reactions [12, 13]. There is also a hypothesis that tumors rich in pancreatic tissue pathologically may extend along the cervical region [5]. In this case, pancreatic tissue was observed in the surgical specimen, supporting this hypothesis.

In this case, the patient initially presented with only neck swelling and right-sided headache, and an elevation in inflammatory markers raised suspicion of cyst infection. Therefore, antibiotic therapy was initiated, and a semi-urgent surgical approach was planned after observing a decrease in inflammatory markers. Although the inflammatory response improved, an increase in neck swelling was noted during the waiting period for surgery. Intraoperatively, adhesions with surrounding tissues were observed, and delaying surgery could have posed a risk of rupture. Therefore, prompt intervention is particularly crucial in cases of mediastinal teratomas extending into the neck.

In this case of a benign mediastinal teratoma, the surgical approach was initially aimed at a less invasive robotic resection in a young patient. However, inflammatory changes in the thoracic cavity necessitated a change to a median sternotomy. In retrospect, starting with a sternotomy may have reduced overall operative time, highlighting the dynamic nature of surgical decisions balancing invasiveness and pragmatism in response to intraoperative conditions.

In our case report, direct extension of the cervicothoracic teratoma into the neck caused obvious inflammatory changes in the thyroid, but other mechanisms than direct infiltration should be considered for thyroid inflammation. One possible mechanism is the release from the teratoma of inflammatory mediators and substances that can affect thyroid tissue even in the absence of direct physical infiltration. These mediators could induce a local inflammatory response in the thyroid gland leading to the observed changes. Furthermore, the proximity of the teratoma to the thyroid gland may trigger an inflammatory cascade even in the absence of direct infiltration. However, no literature could be found to support these considerations.