Enormous thymolipoma: A case report

Thymolipoma is unusual benign mediastinal, slow-growing, encapsulated tumor of the anterior mediastinum with no tendency to recur after a complete surgical excision. Here, we report the case of an adult female who presented with progressive dyspnea of 2 months’ duration especially on lying down. Chest radiograph showed opacity occupying the entire left side. Computed tomography of the chest revealed a large mass on the left side with fat attenuation. Computed tomography-guided biopsy obtained was diagnosed as hyperplasic thymic tissue. The tumor was successfully removed surgically, and histopathological examination confirmed thymolipoma.


Introduction
Thymolipoma accounts for 2-9% of all thymic neoplasm, composed of mature adipose tissue and benign thymic tissue. The majority of these tumors are clinically quiescent; however, they may reach large dimensions and manifest themselves clinically with compression of adjacent structures. Complete surgical excision is curative [1].

Case report
A 21-year-old female patient presented to the hospital with complains of gradually progressive dyspnea of 2 months' duration associated with productive cough. The patient had no history of hemoptysis, loss of weight, loss of appetite, or other constitutional symptoms. Clinically, there was no abnormality detected on general examination. Local examination revealed limitation in chest movement with a decrease in Tactile vocal fremitus (TVF) on the entire left side. On percussion, there was dullness all over the left side, 2, 3, 4, 5 at right midclavicular line and bare area. Chest auscultation detected decreased breath sounds on the left side. Routine blood investigations were within normal limits. A chest radiograph revealed an opacity occupying the entire hemithorax and shifting mediastinum to opposite side (Fig. 1a). A computed tomography scan of the thorax revealed a large mass occupying the entire left side with fat attenuation (−80 to −120 HU) compressing and shifting mediastinal structures to the opposite side (Fig. 1b). Spirometry confirmed the presence of a restrictive defect. Chest ultrasound showed that the echoes in the mass were homogeneous but of higher intensity than those of liver parenchyma with no effusion. Ultrasoundguided tru-cut biopsy was performed, and pathological examination for core biopsy showed lymphoid infiltrate. Flexible bronchoscopy was performed and reported narrowing of the main, lobar, and segmental bronchi (slit like) with intact healthy mucosa. Computed tomography-guided biopsy detected hyperplastic thymic tissue. The patient was referred to the cardiothoracic department. Posterolateral thoracotomy incision (fifth intercostal space) was made. A very large (giant), soft, well-defined, encapsulated mass of about 5 kg, with smooth surface occupying the whole left hemithorax, originating from the thymus gland without any invasion to the adjacent structures, was noticed. Manipulation of the mass was very difficult and so we could not remove it as one structure. Its capsule was opened by means of diathermy and the mass was removed in pieces. Thereafter, we excised the thymus gland with the mass capsule; after mass removal the secondary hypoplastic lung was another problem. We tried to reduce cavity space with positive ventilation of the lung, sixth rib excision, and ablation of the left phrenic nerve. Physiotherapy was started on the first postoperative day with incentive spirometry and exercise training, with oxygen therapy, and applying low suction on chest drains, and followup with clinical examination and chest radiography daily was carried out. The diagnosis was confirmed by histopathological examination as thymolipoma. Ten-month postoperative, the lung filled the pleural cavity and the residual space improved (Figs. 2-5).

Discussion
Thymolipoma is a rare condition with an incidence of about 0.12 cases per 100 000 per year. The first case of a thymolipoma was reported by Lange in 1916 [2]. It appears as a mass composed of mature adipose tissue and benign thymic tissue. The thymic tissue component in thymolipomas is separated by large amounts of mature fat, with no atypia and no mitotic activity. There is no recognized sex predilection. Reported age range is between 3 and 6 years, with a mean age of 22 years [1]. The radiologic features can mimic several conditions, including cardiomegaly, pleural tumors, pericardial effusion, pericardial tumors, basal atelectasis, and pulmonary sequestration. The majority of these tumors are clinically quiescent; however, they may reach large dimensions and manifest themselves clinically by compression of adjacent structures [3]. The pathogenesis of thymolipomas has not been elucidated. Some theories suggest that it is a variant of a thymoma, or hyperplasia of mediastinal fat, or neoplasm of mediastinal fat, which engulfs thymic tissue and      thymic hamartoma; however, the most interesting theory is that a thymolipoma represents a benign tumor of specialized thymic stroma (fat), arising in relationship to the thymic epithelium. [4]. Thymolipomas can occasionally be associated with myasthenia gravis. Histopathological examination revealing admixture of mature adipose tissue and microscopically normal thymus tissue with Hassal's corpuscles is diagnostic [5]. Surgically local resection is curative. There are no reports of recurrence, metastasis, or mortality.

Conclusion
It is important to consider mediastinal tumors in the differential diagnosis of patients presenting with progressive dyspnea without any apparent cardiac illness but chest cardiograph showing enlarged cardiac silhouette [6].

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Conflicts of interest
There are no conflicts of interest.   Jar of excised mass.