Avoiding misdiagnosis of multilocular thymic cysts as malignant tumors on computer tomography

Abstract

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.

Key Words: Thymic tumor, Multilocular thymic cyst, Misdiagnosis, Differential diagnosis, Imaging manifestation, Computed tomography

Core Tip: This editorial provides insights into a recently published clinical case report detailing the experience of a 39-year-old male patient afflicted with a multilocular thymic cyst concurrent with an anterior mediastinal infection. Regrettably, the condition was initially misdiagnosed as a malignant thymic tumor and subsequently managed surgically. Our analysis delves into the factors contributing to this misdiagnosis and outlines enhanced methods for differential diagnosis. It is our hope that this discussion will prompt medical professionals to prioritize imaging-based differential diagnosis and adopt a more comprehensive clinical perspective, thereby reducing the occurrence of clinical misdiagnosis.

INTRODUCTION

Thymic cysts, cystic lesions of the thymus, are relatively uncommon, accounting for only 1%-3% of mediastinal masses[1]. Among them, multilocular thymic cysts (MTCs) represent acquired thymic cysts that develop as secondary lesions due to various inflammatory conditions. It is believed that MTCs often arise from the cystic transformation of structures derived from medullary duct epithelium, such as Hassall's corpuscles, triggered by an inflammatory process[2].

Thymic tumors, originating from thymic epithelial cells, are among the most prevalent mediastinal tumors. These tumors are categorized based on prognosis and the World Health Organization classification system into low-risk thymomas (types A, AB, and B1), high-risk thymomas (types B2 and B3), and thymic carcinomas[3,4]. Surgical intervention is the primary treatment approach for thymic tumors[5]. However, clinical misdiagnosis of MTCs as thymic tumors can occur due to a lack of understanding, potentially leading to unnecessary surgical procedures and associated complications[6].

Currently, computed tomography (CT) stands as the preferred diagnostic modality for evaluating mediastinal tumors, including MTCs and thymic tumors. Through multi-planar reconstruction, CT scans can precisely delineate the lesion's location, size, internal characteristics, and relationship with surrounding structures, aiding in determining the tumor's origin and potential invasiveness[7]. Hence, achieving an accurate CT diagnosis plays a vital role in ensuring the appropriate identification and management of both MTCs and thymic tumors.

CASE SUMMARY

A 39-year-old male patient presented with an irregularly shaped cystic solid mass in the anterior mediastinum, as observed on CT imaging. Mild enhancement of streaks and nodules was noted after contrast administration. Based on these CT findings, the initial diagnosis by the clinician was a malignant thymic tumor. However, postoperative pathological examination revealed a MTC accompanied by hemorrhage and infection[8].

CHALLENGES IN DIAGNOSIS

Comparing CT manifestations of thymic tumors and mediastinal thymic cysts

CT imaging of anterior mediastinal thymic tumors typically reveals a round or ovoid mass in the retrosternal pre-vascular space, exhibiting well-defined borders, uniform density, and slight enhancement during contrast-enhanced scanning. The disappearance of the surrounding fat layer may indicate invasive thymoma, characterized by non-uniform density, a tendency towards cystic degeneration and necrosis, and prominent enhancement of solid components on contrast-enhanced scans[9].

In contrast, thymic cysts commonly present with CT features such as an oval shape, smooth contour, midline positioning, and a lack of visible adjacent thymic tissue[1].

Factors contributing to potential misdiagnosis and the need for improved differential diagnostic techniques

MTCs often exhibit varying protein concentrations, with elevated protein levels, hemorrhage, and inflammation leading to increased CT values within the cystic cavity. When the CT value surpasses 20 Hounsfield units, indicating solid density, there is a risk of misdiagnosis as thymic tumors[6]. Furthermore, the morphological resemblance between MTCs and low-risk thymomas, typically presenting as round or oval shapes, adds complexity to accurate differentiation[10,11].

All in all, distinguishing MTCs from thymic tumors based solely on CT findings can be challenging. Therefore, enhancing preoperative differential diagnostic techniques is imperative to prevent unnecessary treatments.

Recent literature has highlighted several approaches

Biopsy: Utilizing fine needle aspiration, core needle biopsy, or open biopsy for tissue diagnosis is essential[12]. Transthoracic fine needle aspiration is suitable for patients with locally advanced or unresectable thymic tumors, while open surgical biopsy becomes necessary when fine needle aspiration proves inconclusive[13].

Molecular biology: The detection of serum markers such as platelet/albumin ratio, CysC, and Cyfra 21-1 can aid in evaluating the malignant behavior, prognosis, treatment guidance, and follow-up of thymic tumors[14].

Multi-slice CT: Multi-slice CT offers a high detection and diagnostic rate for primary mediastinal thymic tumors, providing clear pathological imaging characteristics[15].

CT functional imaging: As the primary diagnostic modality for mediastinal tumors, CT has evolved with new functional imaging techniques like CT perfusion and spectral CT, offering valuable clinical insights[16,17].

Positron emission tomography/computed tomography molecular functional imaging: Fluorodeoxyglucose positron emission tomography coupled with computed tomography can be utilized as an effective tool for predicting thymic tumor aggressiveness[18].

Magnetic resonance imaging: In differentiating thymic tumors from MTCs, magnetic resonance imaging (MRI) surpasses CT, potentially averting unnecessary thymectomies[19]. Additionally, techniques like diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), and mDixon MRI enhance diagnostic capabilities[20,21].

Radiomics: Radiomics-based nomograms derived from CT scans excel in distinguishing high-density thymic cysts from low-risk thymomas by extracting crucial data and features[11]. This quantitative approach offers valuable insights independent of subjective analysis, aiding in lesion detection, subtype classification, treatment response assessment, and prognostic evaluation.

CLINICAL IMPLICATIONS AND REFLECTIONS

Misdiagnosing thymic cysts as thymic tumors can result in unnecessary surgeries, inflicting mental and physical distress on patients while also escalating their financial burdens.

Thymic tumors, although less common and more intricate, necessitate a comprehensive approach beyond CT imaging alone for accurate differentiation from thymic cysts. Density values of thymic nodules are not definitive indicators of cysts or tumors. Clinicians should employ a combination of diagnostic methods such as biopsy, molecular biology, multi-slice CT, MRI with DWI and ADC to prevent misdiagnosis and inappropriate treatments.

While surgical resection was deemed appropriate for the thymic cyst in this particular case due to its size and compression effects on surrounding tissues, yielding a favorable prognosis, this scenario is an exception. It is crucial to recognize that significant adverse outcomes resulting from misdiagnosis and mistreatment remain prevalent in clinical settings. Hence, the prevention of misdiagnosis and mistreatment poses a formidable challenge for healthcare professionals.

In cases of complex thymic tumors, seeking multidisciplinary consultations when necessary and integrating diverse diagnostic and treatment recommendations can lead to more precise diagnosis and treatment planning.

CONCLUSION

In conclusion, the relatively low incidence of thymic tumors and MTCs has not received significant attention from the medical community. The intricate nature and diversity of thymic tumors contribute to the complexity of their clinical diagnosis and treatment. A comprehensive diagnostic approach, incorporating imaging manifestations, patient demographics, and laboratory tests, can enhance diagnostic accuracy. We urge medical practitioners to prioritize the diagnosis and differential diagnosis of thymic tumors and MTCs, emphasizing the integration of diverse preoperative diagnostic techniques to minimize the risk of clinical misdiagnosis and mistreatment.