Benign primary tumors of the esophagus account for less than 1 % of all esophageal tumors [1]. The most common benign submucosal esophageal tumor is leiomyoma. According to previous reports, leiomyoma accounts for more than half of all benign esophageal tumors [1, 2]. Benign submucosal esophageal tumors also include lipomas, granular cell tumors, and schwannomas. A GIST is an esophageal submucosal tumor with malignant potential.
A few cases of primary esophageal schwannomas have been reported [3, 4]. Gastrointestinal schwannomas account for 0.4 to 1.0 % of all submucosal tumors of the gastrointestinal tract. Most occur in the stomach; the development of a schwannoma in the esophagus is uncommon [4].
The definitive diagnosis of an esophageal submucosal tumor should be made before tumor excision to avoid unnecessary surgery. However, the preoperative pathological diagnosis of a submucosal tumor is unclear in some cases. As in the present case, an adequate specimen is difficult to obtain during biopsy of a submucosal tumor, even if a boring biopsy is performed. This is because the surface of the submucosal tumor is often covered with normal epithelium. EUS-FNAB is now commonly performed to diagnose submucosal tumors. This technique obtains more adequate specimens than does biopsy with upper gastrointestinal endoscopy. Rong et al. [5] reported that the diagnostic accuracy of EUS-FNAB for submucosal tumors was 85.2 % [5]. However, as in our case, EUS-FNAB does not always allow for a definitive pathological diagnosis. We are unsure of the reason for the lack of an adequate specimen in our case. However, a puncture at an acute angle was required to reach the deep portion of the esophageal wall. EUS-FNAB might have been a potentially dangerous procedure in our case because the aortic artery and trachea are located behind the esophagus in the mediastinal space. This may have contributed to the difficulty obtaining the EUS-FNAB specimen in our case. We proposed that the patient undergo EUS-FNAB a third time, but she refused.
Because the preoperative pathological diagnosis was not clear in our case, we performed subtotal thoracoscopic esophagectomy to both treat the patient’s symptoms and possibly diagnose a malignancy. Even if the tumor mass had been a malignancy such as a GIST, the operation would have been curative because we performed subtotal esophagectomy.
Although the final diagnosis in this case was a benign schwannoma, FDG-PET showed a hypermetabolic appearance, suggesting malignant potential. Schwannomas are benign tumors, but a hypermetabolic appearance on FDG-PET has been reported. Schwannomas originate from nerve cells that express glucose transporter type 3 [7], and FDG uptake is considered to be increased for this reason. Beaulieu et al. [7] reported that there was no correlation between FDG uptake and the proliferation rate (Ki-67 index). The authors stated that even if the max SUV is >6.0, a benign schwannoma cannot be excluded. Our case does not conflict with their report in that our benign schwannoma showed a max SUV of 5.5 and MIB-1 labeling index of 10 %. Therefore, FDG-PET could not reveal whether the hypermetabolic appearance indicated a benign or malignant tumor. Otherwise, the findings can be meaningful for a diagnosis of schwannoma.
There is no consensus regarding the surgical treatment of esophageal submucosal tumors. Although the stomach and esophagus differ, the clinical practice guidelines for GIST in Japan declare that surgery is indicated for gastric submucosal tumors larger than 5.0 cm [10]. In our department, we first perform boring biopsy or EUS-FNAB to obtain a histopathological diagnosis of the submucosal tumor. If the submucosal tumor is malignant, such as a GIST, we usually perform a surgical operation. When the histopathological diagnosis is a benign lesion or is unclear, as in the present case, we perform one of the several approaches. If the tumor is small or asymptomatic, we usually perform simple follow-up of the patient. When the tumor is large, increasing in size, or symptomatic, we consider invasive treatment with curative intent.
We usually first try endoscopic treatment for small tumors originating in the submucosal layer. We then attempt enucleation by a thoracoscopic approach because it is less invasive. If the defect of the esophageal wall is expected to be large upon intraoperative examination or the mass has malignant potential, we perform an extended operation based on the individual patient. In this case, we considered open subtotal esophagectomy when the tumor was diagnosed as malignancy or it was difficult to resect it safely and radically.
Thoracoscopic surgery is becoming common [8]. In our department, we believe that thoracoscopic surgery is a good technique for the treatment of benign tumors because it is less invasive and clinically appropriate, especially for benign esophageal tumors. Compared with conventional operations, thoracoscopic esophagectomy for esophageal submucosal tumors is reportedly associated with fewer postoperative complications such as pneumonia and allows for earlier ambulation [11–13]. We selected the thoracoscopic approach to improve our patient’s quality of life and performed subtotal esophagectomy with curative intent.
In conclusion, we have reported a relatively rare case of an esophageal schwannoma. The diagnosis was difficult because we could not obtain an adequately sized specimen by boring biopsy and EUS-FNAB. The thoracoscopic approach is a good treatment option for large submucosal tumors of the esophagus.
