Rapidly growing mediastinal mature cystic teratoma with increased FDG uptake: challenging the paradigm of indolent growth

Abstract

Background

Mature cystic teratomas of the mediastinum are typically germ cell tumors with indolent growth, with documented annual growth rates often less than 5 centimeters. We report a case with an abnormal growth rate (Average diameter growth rate 7.14 mm/month) and significant increased 18 F fluorodeoxyglucose (18 F FDG) uptake, which challenges conventional diagnostic concepts.

Case presentation

A 34-year-old female presented with progressive chest tightness. Serial CT imaging revealed a right anterior superior mediastinal mass that grew from approximately 1.5 cm in long diameter to 6.5 cm over 7 months (Average diameter growth rate 7.14 mm/month). 18 F fluorodeoxyglucose Positron Emission Tomography-Computed Tomography(18 F-FDG PET/CT) revealed the lesion with high metabolic heterogeneity, and the maximum standardized uptake value (SUVmax 6.9). Pathological examination after thoracoscopic-assisted complete resection confirmed the diagnosis of mature cystic teratoma with mature glial components.

Conclusion

This case suggests that lesions with rapid growth and significantly increased FDG uptake do not necessarily indicate malignant transformation of teratoma. Multidisciplinary decision-making should be based on dynamic quantitative imaging and metabolic feature analysis.Categories: Pathology, Oncology, Pulmonology.

Introduction

Mediastinal mature cystic teratomas account for 80% of mediastinal germ cell tumors, and the age distribution is mainly concentrated in those under 30 years old [1]. Their growth kinetics have long been described as “inert” (annual growth rate < 5 mm). However, this understanding is primarily based on small sample retrospective studies, lacking large sample and long-term follow-up prospective studies, making it difficult to accurately describe the growth kinetics of mediastinal mature cystic teratomas.

The value of FDG-PET in the differential diagnosis of mediastinal masses is increasingly prominent, and it is generally believed that an SUVmax > 5.0 suggests a risk of malignancy [2]. This case report quantitatively describes a mediastinal mature teratoma with a growth rate of >7 mm/month, whose FDG metabolic level overlaps with that of malignant tumors but lacks histological evidence of malignancy. This finding challenges traditional perceptions and provides a new dimension for clinical decision-making.

Case presentation

This case report quantitatively describes a mediastinal mature teratoma with a growth rate of >7 mm/month, whose FDG metabolic level overlaps with that of malignant tumors but lacks histological evidence of malignancy. This finding challenges traditional perceptions and provides a new dimension for clinical decision-making. In February 18th, 2024,a 37-year-old female patient presented to our hospital with “chest tightness for 20 days without obvious cause”. The patient denied accompanying symptoms such as chest pain, cough, fever, or weight loss. In her past medical history, she had been scheduled for surgery at another hospital 7 months prior due to thyroid nodules, during which a preoperative chest Computed Tomography (CT) incidentally revealed a small anterior mediastinal mass (without definitive diagnosis), but no further intervention was performed (see Fig. 1A). There was no history of smoking, family history of malignancy, or special environmental exposure. Collecting venous blood samples for tumor marker examination showed that CEA (Carcinoembryonic antigen) was 1.43 ng/ml, NSE (Neuron-specific enolase) was 14.80 ng/ml, CYFRA21-1 (Cytokeratins-19) was 1.21 ng/ml, and Pro-GRP (Pro-Gastrin-Releasing Peptide) was 30.40 pg/ml. All of these were within the normal range. After admission, the patient underwent relevant examinations, among which chest enhanced CT showed a heterogeneous density mass (6.5 × 4.9 cm) in the right anterior superior mediastinum (see Fig. 1B). The patient’s PET-CT results showed further improvement, demonstrating focal FDG uptake in the solid component (SUVmax 6.9). No significantly hypermetabolic lymph nodes were observed in the mediastinum or bilateral hilar regions, and no distant metastases were detected. (see Fig. 2A and B).

Fig. 1.

Growth image comparison. The CT images were taken on July 10, 2023 (A) and February 19, 2024 (B) respectively

Fig. 2.

Preoperative PET CT image shown. (A-B) The Fluorodeoxyglucose positron emission tomography (FDG-PET) shows increased uptake (red arrow)

The patient participated in a multidisciplinary consultation, considering the abnormal growth rate of the mass (an average increase in the longest diameter of about 7 mm/month over 7 months) and the high metabolic characteristics of FDG, The multidisciplinary consultation, based on the patient’s dynamic imaging changes and metabolic characteristics, recommended direct surgical intervention with further pathological examination during the procedure. After comprehensive consideration of the consultation opinions and the patient’s family’s preferences, we planned to perform thoracoscopic-assisted right anterior mediastinal tumor resection combined with thymectomy. During the operation, it was found that the right anterior superior mediastinal mass had invaded the right thoracic cavity and involved part of the right upper lobe, causing inflammatory changes. During the operation, we dissected along the surgical outer membrane, carefully preserving the pericardium, intrathoracic arteries and veins, and the superior vena cava, and completely resected the mediastinal tumor and thymus. Finally, the inflammatory lung tissue in the right upper lobe of the lung involved by the tumor was continuously closed and excised using an electric linear cutting suture device. Regarding pathological sampling, intraoperatively we marked high metabolic areas on imaging with sutures as a reference for postoperative pathological sampling. The gross postoperative pathology revealed a cystic-solid mass ( 9 × 10 × 3 cm), which was a mature cystic teratoma, and mature glial components were detected (see Fig. 3A and C). The patient was discharged smoothly on the 6th day post-operation without complications. A follow-up chest CT one month later showed no recurrence (see Fig. 3B), and the symptom of chest tightness was completely alleviated.At present, the patient has been followed up for 1 year post-surgery, and the post-operative check-up indicates a good recovery with no signs of recurrence.

Fig. 3.

Preoperative and postoperative CT images comparison as well as pathological images. The left (A) and right (B) sides represent the preoperative and postoperative CT images respectively. (C) Postoperative mass observed under the microscope. Representative diagram of histopathology

Discussion and conclusion

This case presents two major special characteristics: rapid growth cycle and malignant metabolic characteristics.The progression growth cycle was within 7 months, with a growth rate greater than 7 millimeters per month. The potential mechanisms include (1) the paracrine effect of oral levothyroxine sodium after thyroid nodule surgery (the patient has thyroid surgery combined) or activation of the Wnt/β-catenin pathway in the colloidal component [3], (2) this case shows a special metabolic characteristics: The SUVmax of this patient exceeds 95% of benign teratoma patients, witch is usually 1.5–3.2, (3) in terms of literature reports: there are limited cases documenting similar rapid - We searched for the only 4 cases of rapidly growing mediastinal mature teratomas (Table 1), and considering their distribution characteristics, it is believed that the more vigorous cellular metabolism in young adults may also be a significant factor in their rapid growth. The possible explanations included the metabolic activity of neuroglial tissue and the subclinical inflammation due to micro-rupture.This case indicates that growth rate can’t be used as an absolute diagnostic criterion for benignity or malignancy and high metabolic lesions need to be combined with pathology rather than judged as malignant alone.We need to be extra cautious in determining surgical indications, even if considering benign tumors, regular CT examinations are necessary. It is suggested that “growth rate > 5 mm/month” be included as a surgical indication and multicenter studies be conducted to optimize treatment strategies. Meanwhile, this case demonstrates that even mature teratomas can exhibit invasive imaging features, so for tumors adjacent to important structures such as pericardium and lung tissue, we should still consider aggressive surgical resection.

Table 1.

The reports of rapidly growing mediastinal mature teratomas

Research (Year)	Age/Gender	Duration of progression	SUVmax range	Symptom	References
Omachi N et al.	23/male	4 months	4.9	Dyspnoea	[4]
Fujita K et al.	17/femle	16 months	Unlabeled values	Chest discomfort	[5]
Hussain SA et al.	27/male	5 Days	Unlabeled values	Chest pain	[6]
Uyama T et al.	12/female	14 months	Unlabeled values	Chest pain	[7]
Current cases	32/femle	7 months	6.9	Chest tightness

Author contributions

Xiaohe Hao is the corresponding author. Zhigang Shi conceived of the study and participated in its design and coordination. All authors read and approved the final manuscript.

Funding

Not applicable.

Data availability

Data availability and materials is not applicable to this article as no new data were created or analyzed in this study.

Declarations

Ethics approval and consent to participate

The study protocol was approved by the Institutional Review Board of Shandong Cancer Hospital and Institute. Written informed consent was obtained from the patient relatives for publication of this study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.