Thoracoscopic Approach for Treating a Primary Hydatid Cyst in the Thymus in a Teenager: A Case Report

Introduction

Hydatid disease is a zoonotic parasitic infection caused by Echinococcus granulosus [1]. It remains a major clinical concern in endemic regions, with an estimated annual incidence of 2 to 3 million cases worldwide [1,2]. In endemic regions, the incidence can reach 50 cases per 100 000 annually [2].

The life cycle of this disease consists of a definitive host (most commonly dogs) and an intermediate host (usually sheep) [3]. Humans can become infected through fecal-oral route by ingesting food contaminated with eggs in the feces of the definitive host [2,3].

In humans, the liver is the most affected organ, followed by the lungs [3]. Although hydatid disease can affect nearly any part of the body, it rarely involves the mediastinum, with reported incidence of (2.6%) among affected individuals [3]. Within the mediastinum, the posterior mediastinum is the most frequent site [3]. However, hydatid cysts of the thymus are even more uncommon [4], with only 12 cases of hydatid cyst in thymic gland reported up to 2012 [5].

Most cases remain asymptomatic until complications arise, such as rupture, which can lead to anaphylactic shock or infection, or until symptoms develop due to compression of surrounding structures by enlarging cysts [3,4,6]. Other cases are diagnosed incidentally [4].

The therapeutic options for hydatid disease consist of surgical treatment and pharmacological treatment. Surgical treatment is always indicated for large cysts [2,7], while pharmacological treatment is indicated before and after surgery [2,7].

Managing such cases poses a significant challenge, not only due to the difficulty in reaching the diagnosis given the nonspecific clinical findings, but also because performing thoracoscopic surgery for a huge cyst in a limited space with vital structures like the mediastinum is technically demanding. The aim of this report is to raise awareness of this rare location of a hydatid cyst, which can present both diagnostic and therapeutic challenges, by describing the case of a 17-year-old male patient presenting with isolated hydatid cyst in the left hemithorax, originating from the thymus. Both the cyst and thymic tissue were resected using video-assisted thoracoscopic surgery (VATS).

Case Report

Procedure and Techniques

ANESTHESIA:

After the induction of general anesthesia, double-lumen endotracheal intubation was established. Fiberoptic bronchoscopy was performed to ensure proper tube placement. During surgery, the left lung was isolated and CO₂ gas was insufflated to the left hemithorax with minimal pressure to optimize the working space.

POSITION OF THE PATIENT:

The patient was positioned in semi-supine position; the left hemithorax was elevated by approximately 30-degrees using a roll placed under the ipsilateral side of the chest. The left upper extremity was flexed and internally rotated to expose the lateral chest wall, ensuring the area would not interfere with surgical instruments.

PORT PLACEMENT:

The surgery was planned to be performed as triple-port surgery. The first 10-mm trocar was placed in the 5^th intercostal space (ICS) in the midaxillary line (MAL). CO₂ gas was insufflated into the left hemithorax with a pressure of 8 mmHg. Under thoracoscopic view, using a 10-mm 30-degree camera, the other 2 trocars were inserted – a 5-mm trocar was inserted at the 5^th ICS anterior-axillary line (AAL), and another 5-mm trocar was inserted at the 6^th ICS along the midclavicular line.

PROCEDURE: Upon insertion of the camera, we encountered a large cystic lesion originating from the mediastinum and not attached to the left lung (Figure 3). A laparoscopic aspiration needle was used to evacuate the cyst (Figure 4), which revealed a watery material. The needle was then left in place and used to instill hypertonic saline (NaCl 3%), which was later aspirated. We irrigated the left hemithorax with NaCl 3%. Then, the evacuated cyst was wrapped using a non-traumatic laparoscopic forceps to prevent any spillage and to optimize the working space (Figure 5).

After identification of the major landmarks, dissection was started caudally over the pericardium using a 5-mm curved-jaw laparoscopic tissue sealer from Ethicon (Enseal). After that, the left phrenic nerve was identified and a dissection plane between the cyst and the nerve was achieved using laparoscopic scissors to avoid any thermal injury to the nerve (Figure 6).

The left internal thoracic blood vessels were then identified and preserved while we began the retrosternal dissection of the cyst. Our attempt to separate the cyst from the thymus was unsuccessful, as the cyst was occupying most of the thymus. Given that the cyst originated from the thymic gland, an en bloc resection of the cyst with a thymectomy was performed to ensure complete resection of the cyst and to prevent recurrence.

During dissection, the innominate vein was identified. The thymic veins were divided using an energy device (Enseal) and endoscopic clips. Then, the whole specimen was retrieved using a laparoscopic Endo-bag. Gross examination of the specimen revealed a thymic gland with a cyst that had a laminated membrane. After controlling hemostasis, a 28-Fr chest tube was placed in the left chest cavity and all wounds were closed in layers. The final diagnosis was confirmed by histopathological examination, which showed thymic tissue along with an embedded hydatid cyst (Figure 7).

POSTOPERATIVE COURSE:

The postoperative course was uneventful. Two days later, the chest tube was removed, then he underwent a CXR (Figure 8). Later, he was discharged home on albendazole 400 mg twice daily, and he has been on regular follow-up for 1 year without any clinical or radiological sign of recurrence.

Discussion

Hydatid disease is a clinically important zoonotic infection that primarily affects the liver and lungs [3]. However, extrapulmonary intrathoracic hydatid disease is very uncommon, with the mediastinum being affected in 2.6% of cases [3]. The thymus is rarely involved by hydatid disease, even in endemic areas [4]. With this report, we aim to raise awareness of this rare location of a hydatid cyst, which can complicate the diagnostic evaluation and therapeutic approach.

In patients with negative serological tests, it is challenging to distinguish hydatid cysts from other mediastinal cysts, both clinically and radiologically [4]. However, eosinophilia in laboratory results may indicate a parasitic infection like echinococcosis [2,8]. CT scans are helpful in diagnosing hydatid cyst disease and are essential in evaluating the anatomical relationship of the cyst before surgery [4].

Harmouch et al reported only 12 cases of thymic hydatid cysts up to 2012 [5]. To the best of our knowledge, there are no other reported cases after that date. None of the reported cases were managed with VATS. One of the reported cases underwent neck exploration to excise the mass with thymic gland [5]. Another case underwent left thoracotomy to remove a 7×7.5 cm cystic lesion that was bulging to the left hemithorax [4].

The management for these cases includes total excision followed by anti-helminthic medication like albendazole in the postoperative period [1,3].

The standard surgical approach for thoracic hydatid disease is thoracotomy, as it provides adequate exposure with minimal risk of spillage [9]. However, thoracoscopic surgery is gaining acceptance in treating various thoracic conditions, including malignant diseases.

Cai et al found that treating lung hydatid disease with VATS had advantages over thoracotomy in terms of length of surgery, intraoperative blood loss, postoperative drainage volume, and length of hospital stay [9]. A meta-analysis also found that VATS has advantages over thoracotomy in patients with pulmonary hydatid disease, but found that VATS carried a higher risk of postoperative atelectasis [10].

Conclusions

Although extrapulmonary intrathoracic hydatid disease is uncommon, it should be kept in mind as a potential differential diagnosis for any cystic lesion in the anterior mediastinum, especially in endemic regions. Minimally invasive surgery offers a safe and effective treatment option in selected cases of hydatid cyst, especially when followed by postoperative medical therapy.