Unraveling the role of ectopic thymic tissue in patients undergoing thymectomy for myasthenia gravis

Abstract

Extended thymectomy has been considered the goal of surgery for myasthenia gravis (MG) mainly due to the existence of ectopic thymic tissue. Recently, ectopic thymic tissue has attracted increasing attention in patients with MG following thymectomy. However, the specific role of ectopic thymic tissue in patients with MG is still under debate. A systematic search of the literature was performed on PubMed and Medline according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISM) statement. Studies evaluating the rate of ectopic thymic tissue in patients with MG with or without thymoma were included. Extraction was performed for all eligible studies and the rate of ectopic thymic tissue at common locations was calculated. Eighteen out of fifty-nine studies were eligible for inclusion, of which ten studies reported the common locations of ectopic thymic tissue in mediastinal fat. Of these ten studies, the presence of ectopic thymic tissue was investigated in different anatomical locations in 882 patients, of whom, 509 patients (58%) have at least one positive location with the most common ones being anterior mediastinal fat, pericardiophrenic angles, aortopulmonary window, cervical region (pretracheal fat) and lateral to phrenic nerves. On the other hand, nine studies analyzed the influence of the presence of ectopic thymic tissue on the clinical outcomes of MG patients. Of these, six found that the presence of ectopic thymic tissue in MG patients is a significant predictor of poor outcome after thymectomy, however, the other three did not find a significance. Altogether, ectopic thymic tissue is likely to present in more than a half of patients undergoing thymectomy for MG. Besides, MG patients who have ectopic thymic tissue after thymectomy do not seem to have as good outcome as those who have not.

Subxiphoid thoracoscopic thymectomy for myasthenia gravis

“…However, it is presumed that a post-thymectomy myasthenia crisis might be ascribed to the residual or ectopic thymic tissue. A review showed that the common locations of ectopic thymic tissue in mediastinal fat included anterior mediastinal fat (33.2%), pericardiophrenic angles (13.6%) and an aortopulmonary window (10.4%) [ 9 ]. Some anatomical sites (such as the pericardia-phrenic angle) might be difficult to access under the subxiphoid approach.…”

Technique for ectopic intrathymic parathyroid adenoma: the uniportal subxiphoid approach

“…As in surgical resection of thymic pathologies, the phrasing ‘the more complete the resection, the better the clinical outcome’ is also in the resection of MEPAs rather a command than an advice [ 7 , 12 ]. Of course, basic prerequisite for any surgical success are excellent preoperative imaging studies, which definitely contributed to the high success rate of parathyroidectomy in the cure of PHPT [ 13 , 14 ].…”

An ectopic thymoma arising in the middle mediastinum that was difficult to distinguish from a lymph node metastasis

“…An ectopic thymus can occur due to the failure of migration during embryological development [8]. Li et al [10] summarized ten studies and reported common locations of ectopic thymic tissue in mediastinal fat in patients with myasthenia gravis. Moreover, the presence of ectopic thymic tissue was investigated in different anatomical locations in 882 patients, with 509 (58%) having at least one positive location.…”