European Journal of Cardiovascular Medicine

Thymomas are uncommon tumors of thymic epithelial origin, typically arising in the anterior mediastinum and frequently associated with myasthenia gravis¹. Aberrant embryological descent of the thymus can leave ectopic thymic rests along its migratory pathway, which may rarely undergo neoplastic transformation². Ectopic thymomas have been reported in several unusual locations; however, paravertebral presentations are exceptionally rare and often mimic neurogenic or paraspinal tumors on imaging³,⁴.

We present a rare case of a Type B2 thymoma presenting as a right paravertebral extrapleural mass, highlighting the diagnostic challenge and the importance of considering ectopic thymoma in the differential diagnosis of paravertebral lesions¹,⁵

A 52-year-old male presented with history of breathlessness since 2–3 months which was exaggerated on lying down. The patient was a known case of thymoma operated on 03/11/2014 and had associated myasthenia gravis, for which he was on Tab Distinon 60 mg twice daily and Tab Azoran 50 mg twice daily⁶. The patient underwent CT scan of the chest, which showed a homogeneously enhancing mass approximately 3.2 × 4.6 cm in size, a well-marginated extrapleural lesion in the right paravertebral region between D8 to D10. The lesion showed mixed attenuation with solid and cystic components, with no underlying bone erosion or destruction. A tiny calcific speck was noted within the lesion³,⁴. CT-guided biopsy revealed a cellular tumor composed of epithelioid cells with distinct nucleoli at places with interspersed lymphoid cells. Intervening thin-walled vessels with perivascular hyalinization were noted. On immunohistochemistry, the epithelioid cells were highlighted by AE1/AE3 (diffuse, strong) and PAX8 (diffuse, weak), while interspersed lymphoid cells were highlighted by CD3 and TdT. Overall features were consistent with thymoma, favoring Type B2¹,⁵. The patient was hospitalized and acetylcholine receptor antibody testing showed >80.0 nmol/L (positive >0.50). The patient received IVIg for 5 days and was then posted for surgery in view of associated myasthenia gravis⁶. The patient underwent surgical resection of the tumor through a right-sided thoracotomy via the 6th intercostal space. The mass was seen on the posterior aspect of the ribs between D8 and D10 measuring about 7 × 5 cm and was firm in consistency. The mass was excised and sent for histopathological examination. The thoracotomy site was closed with a chest tube placed in the right hemithorax. Postoperatively, the patient had an uneventful recovery and was discharged on postoperative day 7 after a 5-day course of antibiotics⁷,⁸. Histopathological examination showed a tumor surrounded by a thick fibrous capsule composed of nodules and sheets of polygonal epithelial cells closely admixed with an almost equal proportion of lymphocytes. The polygonal epithelial cells possessed centrally placed, round to oval vesicular nuclei and moderate eosinophilic and clear cytoplasm. The epithelial cells expressed cytokeratin and PAX8 and were immunonegative for CD5, while lymphocytes expressed CD3 and TdT, confirming the diagnosis of thymoma, Type B2¹,⁵.

Ectopic thymomas are rare tumors arising from aberrant thymic tissue left along the embryological migratory pathway of the thymus². While thymomas typically occur in the anterior mediastinum, ectopic presentations in paravertebral locations are exceptionally uncommon and often pose a diagnostic dilemma due to their radiological resemblance to neurogenic or paraspinal tumors³,⁴

Radiologically, paravertebral thymomas lack specific distinguishing features and may mimic a wide range of posterior mediastinal or paraspinal lesions³,⁴. Hence, histopathological examination with immunohistochemistry remains essential for definitive diagnosis¹,⁵

Complete surgical excision remains the cornerstone of treatment for localized thymoma irrespective of its location and offers excellent outcomes when achieved with clear margins⁷,⁸. The association with myasthenia gravis necessitates careful perioperative optimization, as illustrated in this case by preoperative IVIg therapy and uneventful postoperative recovery⁶.

Paravertebral ectopic thymoma is an exceptionally rare entity that can closely mimic more common paraspinal tumors³,⁴. This case underscores the importance of considering ectopic thymoma in the differential diagnosis of paravertebral masses, particularly in patients with myasthenia gravis or prior thymoma⁶.Accurate diagnosis relies on histopathology and immunohistochemistry¹,⁵, and complete surgical excision remains the definitive treatment

with favorable outcomes⁷,⁸

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