This editorial provides insights from a case report by Sun et al published in the World Journal of Clinical Cases. The case report focuses on a case where a multilocular thymic cyst (MTC) was misdiagnosed as a thymic tumor, resulting in an unnecessary surgical procedure. Both MTCs and thymic tumors are rare conditions that heavily rely on radiological imaging for accurate diagnosis. However, the similarity in their imaging presentations can lead to misinterpretation, resulting in unnecessary surgical procedures. Due to the ongoing lack of comprehensive knowledge about MTCs and thymic tumors, we offer a summary of diagnostic techniques documented in recent literature and examine potential causes of misdiagnosis. When computer tomography (CT) values surpass 20 Hounsfield units and display comparable morphology, there is a risk of misdiagnosing MTCs as thymic tumors. Employing various differential diagnostic methods like biopsy, molecular biology, multi-slice CT, CT functional imaging, positron emission tomography/CT molecular functional imaging, magnetic resonance imaging and radiomics, proves advantageous in reducing clinical misdiagnosis. A deeper understanding of these conditions requires increased attention and exploration by healthcare providers. Moreover, the continued advancement and utilization of various diagnostic methods are expected to enhance precise diagnoses, provide appropriate treatment options, and improve the quality of life for patients with thymic tumors and MTCs in the future.

This case report details a rare thymic basaloid carcinoma initially misinterpreted as a mediastinal teratoma, underscoring the diagnostic challenges posed by such tumors. A 71-year-old female presented with an asymptomatic anterior mediastinal tumor discovered incidentally during a routine health examination. Surgical intervention, followed by pathological and immunohistochemical analysis including CK-pan, p63, p40, and CD117 molecules, led to a definitive diagnosis of basaloid carcinoma of the thymus. This case highlights the critical importance of differential diagnosis in mediastinal lesions, especially those presenting with multilocular thymic cysts on chest CT. The subxiphoid video-assisted thoracoscopic surgery enabled complete tumor resection with minimal trauma and favorable postoperative outcomes. The patient opted against further radiotherapy or chemotherapy and she has survived for over eight months without recurrence. This case report contributes to the growing understanding of thymic basaloid carcinoma, a rare and potentially aggressive thymic carcinoma subtype. It emphasizes the necessity for precise surgical techniques and enhanced diagnostic acumen among cardiothoracic surgeons and oncologists.

BACKGROUND: Multilocular thymic cyst (MTC) is a rare mediastinal lesion which is considered to occur in the process of acquired inflammation. It is usually characterized by well-defined cystic density and is filled with transparent liquid.
METHODS: We report on a 39-year-old male with a cystic-solid mass in the anterior mediastinum. Computer tomography (CT) imaging showed that the mass was irregular with unclear boundaries. After injection of contrast agent, there was a slight enhancement of stripes and nodules. According to CT findings, it was diagnosed as thymic cancer.
CONCLUSIONS: After surgery, MTC accompanied by bleeding and infection was confirmed by pathological examination. The main lesson of this case was that malignant thymic tumor and MTC of the anterior mediastinum sometimes exhibit similar CT findings. Caution is necessary in clinical work to avoid misdiagnosis.

Multilocular thymic cysts (MTC) are acquired multilocular cysts caused by inflammation. The rarity of such lesions and a lack of recognition make diagnosis and treatment difficult. Herein, we present our experience with a multilocular mediastinal cyst that resulted in the development of thymic cancer with metastasis over a period of 13 years. Computed tomography findings revealed an anterior mediastinal mass that was suspected to be an MTC in a 49-year-old man. The mass shrank gradually over a period of 7 years; however, growth was observed at 10 years after initial detection. At 13 years after detection, thymic carcinoma with multiple lung metastases was diagnosed. Resection was recommended during the follow-up period, but the patient refused treatment. A multilocular wall and location are factors that indicate MTC. However, even if a definitive diagnosis is not made, resection of multilocular anterior mediastinal cysts should be considered as determining the preoperative diagnosis is difficult. Nevertheless, our case suggests that the coexistence of tumors with cysts is possible, and the potential for malignant tumor development exists.

A multilocular thymic cyst (MTC) is a rare mediastinal tumor with multiloculated cyst-like structures in the anterior mediastinum. This tumfor is associated with inflammatory diseases, including human immunodeficiency virus (HIV) infection. The present study reports a case of MTC detected during coronavirus disease 2019 (COVID-19) treatment in an adult who was tested HIV positive. An anterior mediastinal tumor was incidentally detected on computed tomography in a 52-year-old man with a 20-year history of HIV infection on the 9th day of COVID-19. The patient was asymptomatic with no notable physical findings. Magnetic resonance imaging revealed a 28-mm bilocular cyst. Robot-assisted thoracoscopic tumor resection was performed. Pathological examination showed that the cyst was lined with squamous or cuboidal epithelium, and the cystic lesion wall was mainly composed of thymic tissue with follicular hyperplasia. Based on these findings, the patient was diagnosed with MTC. To date, only 15 MTC cases have been reported in patients with HIV, and the majority of cases showed HIV infection-related symptoms such as lymphoid interstitial pneumonia and parotid gland enlargement. The present case was atypical for an HIV-related MTC because it did not involve HIV infection-related symptoms, suggesting the possibility for an alternative etiology such as COVID-19. Further reports on MTC development in patients with COVID-19 are required to elucidate the relationship between MTC and COVID-19.

Multilocular thymic cysts (MTCs) in adults with human immunodeficiency virus (HIV) are rarely reported.
We describe a case of symptomatic MTC in a male with untreated HIV. A presumptive diagnosis was established based on radiographic imaging and biopsy. Pathologic diagnosis and exclusion of malignancy were ultimately confirmed following thymectomy. In conjunction with starting antiretroviral therapy, the patient recovered well post-operatively with a resolution of his presenting symptoms.
Our case report and review of the literature serve to highlight MTCs as an important clinical entity occurring in persons with HIV.

The multilocular thymic cyst (MTC) is a rare, acquired disease caused by inflammatory changes in the thymus, and is associated with autoimmune diseases. We report a case of MTC with thrombocytopaenia, which improved following surgical resection. A 45-year-old man developed thrombocytopaenia with an anterior mediastinal tumour. Thrombocytopaenia due to an autoimmune mechanism, associated with thymoma or thymus-related disease, was suspected. Pathologic analysis following thoracoscopic thymectomy confirmed MTC. The platelet level recovered postoperatively. Our findings suggested a relationship between the acquired formation of MTC and the development of autoimmune antibodies. However, further investigation is needed to obtain more information.

Multilocular thymic cyst (MTC) and germ cell tumors are common diseases that impact the mediastinum. Correctly diagnosing these diseases can be difficult because several other conditions can mimic them. We report a male patient with MTC associated with mediastinal seminoma. A needle biopsy of the mediastinal tumor revealed numerous epithelioid cell granulomas that mimicked sarcoidosis or mycobacterial infection. However, large atypical cells positive for Oct3/4 and KIT were noted between the granulomas; thus, we diagnosed the patient with mediastinal seminoma. The resected tumor, after chemotherapy, consisted of multiple cystic lesions, and a residual germ cell tumor was first considered. However, thymic medulla-specific elements, namely, POU2F3-positive thymic tuft cells and rhabdomyomatous myoid cells accompanying the epithelium, led to the correct diagnosis of MTC. Our case underscores the importance of recognizing the histological features associated with mediastinal seminoma and provides novel findings for MTC pathogenesis, namely, the presence of thymic tuft cells.

We encountered a rare case of thymic cyst accompanied by mediastinitis. A 39-year-old Japanese male presented with fever and chest pain. The chest CT revealed a mass composed of a lobular cystic lesion with inflammation, suggesting the onset of mediastinitis. A definitive histological diagnosis was not obtained, and we performed a thymectomy. Pathologically, the thymic cyst was accompanied by multiple cavities, mimicking thymic cysts, caused by the inflammatory abscess. The surrounding adipose tissue showed inflammatory cell infiltrations with chronic fibrosis. These findings indicate that clinicians should be aware that thymic cysts may cause severe mediastinitis.

BACKGROUND: Multilocular thymic cyst (MTC) is a rare condition of an acquired multilocular cystic lesion caused by inflammation and often associated with autoimmune diseases or malignant tumors. We present a patient with MTC and asymptomatic rheumatoid arthritis (RA), which is termed preclinical RA.
METHODS: A 60-year-old man underwent a computed tomography scan, which revealed an 8.5 cm multilocular cystic lesion in the anterior mediastinum. The tumor had a lower intensity on T1-weighted imaging and a higher intensity on T2-weighted imaging. The imaging did not only suggest an MTC, but also the possibility of a thymoma with cystic degeneration, or lymphoma. We performed an extended thymectomy via median sternotomy. The lesion was diagnosed as MTC based on histopathological findings. Laboratory tests were performed for the purpose of screening for autoimmune diseases. He was diagnosed with preclinical RA, since the anti-cyclic citrullinated peptide antibody (ACPA) was positive.
CONCLUSIONS: Specificity of ACPA is recorded in over 90% of patients with RA; ACPA is positive in about 40% of patients with preclinical RA. As patients with preclinical RA are more likely to develop RA, careful follow-up is required. Early diagnosis and treatment of RA can prevent destruction of joints, thereby preventing irreversible disability.
CONCLUSIONS: In patients with MTC, evaluating the cause of the inflammation, such as autoimmune diseases, is essential. Further studies are required to investigate the relationship between MTC and preclinical RA.