Fluorine-18-fluorodeoxyglucose uptake in a benign oesophageal leiomyoma: a potential pitfall in diagnosis

Abstract

Positron-emission tomography scans (PET) with fluorine-18-fluorodeoxyglucose (¹⁸F- FDG) are usually negative in leiomyomas. Two patients underwent a PET that showed an increased ¹⁸F- FDG uptake of the distal oesophagus suggestive for malignancy. Both patients were operated on and histologic examination revealed a benign leiomyoma in both cases. We conclude that oesophageal leiomyomas are a potential cause of a false-positive PET. A high level of caution is needed in these diagnostically challenging cases to prevent unnecessary surgical procedures.

INTRODUCTION

Leiomyoma is a common benign tumour of the oesophagus. Definitive diagnosis can only be made by histologic examination. Nevertheless, a preoperative endoscopic mucosal biopsy is a risk factor for mucosal injury [1] and therefore not advised. To narrow the differential diagnosis several diagnostic tools as barium swallow, endoscopy, endoscopic ultrasonography, computer tomography (CT) and magnetic resonance imaging (MRI) are used.

Positron-emission tomography scans (PET) with fluorine-18-fluorodeoxyglucose (¹⁸F- FDG) are usually negative in leiomyomas as they provide a functional assessment of cellular activity in a neoplasm with low mitotic activity. We describe two cases of a PET-positive oesophageal submucosal tumour suggesting malignancy, where pathologic examination confirmed a benign leiomyoma.

CASE 1

A 41-year old woman was seen in follow-up after surgical treatment with radio- and chemotherapy for an adenocarcinoma of the right breast. A CT scan of thorax and abdomen was performed because of unspecific pain. It showed a circular thickening of the distal oesophageal wall suggestive for malignancy. The patient was eating well and did not have complaints of regurgitation or reflux. Endoscopic evaluation showed a normal mucosa, suggesting an oesophageal submucosal lesion or external compression. Endoscopic ultrasound revealed a suspect submucosal lesion near the cardia. PET showed an intense ¹⁸F- FDG uptake of the distal oesophagus (Fig. 1). Repeated endoscopic fine needle aspiration could not confirm malignancy, but based on the PET findings the lesion was still suspect for malignancy [e.g. gastrointestinal stromal tumour (GIST)]. An exploratory left thoracotomy was performed and macroscopic evaluation showed the typical features of a benign leiomyoma. Enucleation was performed and pathology confirmed this diagnosis.

Figure 1:

Case 1: CT and PET through the mass in the distal oesophagus (arrows).

CASE 2

A 27-year old woman with progressive dyspnoea and pain in the left upper abdomen underwent a chest X-ray which showed an additional structure in the posterior cardiophrenic angle. Subsequent evaluation showed contradictory features. The barium swallow showed an ulcerated tumoral process suggestive for leiomyo(sarco)ma or GIST. The first endoscopic evaluation showed an oesophagitis grade B with a small mucosal defect and a possible small diverticulum. CT showed a mass of 5 cm near and posterior of the distal oesophagus, suggestive for a leiomyoma or a duplication cyst. MRI was suggestive for a leiomyoma or a teratoma. Repeated endoscopic evaluation showed a normal oesophageal mucosa without any defect. Endoscopic ultrasound suggested the image of a GIST; however, the image was not typical for it. PET showed a discrete ¹⁸F- FDG uptake of the lesion (Fig. 2). Histology taken by endoscopic ultrasound guided biopsy could not reveal malignancy.

Figure 2:

Case 2: CT and PET through the mass in the distal oesophagus (arrows).

A left thoracotomy was performed with enucleation of the tumour. Frozen section confirmed a myxoid-type leiomyoma without arguments for malignancy.

In both cases, the subsequent post-operative evolution was uneventful and the patient was discharged on day 8 post-operatively.

DISCUSSION

PET is playing a very important role in the evaluation of tumours. The idea that any abnormal activity of cells as in malignancies or inflammation is detectable by measuring the consumption of glucose is an incredible advantage against the morphologic assessment by CT or MRI. However, PET is not infallible and has its false-positive results as any other diagnostic tool has, especially when ¹⁸F- FDG accumulations are incidental findings.

Gastro-oesophageal reflux, Barrett oesophagus, glycogen acanthosis and infection are causes of abnormal ¹⁸F- FDG uptake in benign inflammatory lesions [2]. In fact, the accumulation of ¹⁸F- FDG in the distal oesophagus is not infrequent and Roedl et al. [3] reported only 8.3% malignancy in incidental oesophageal ¹⁸F- FDG uptake. Heusner et al. [4] even postulated that an abnormal ¹⁸F- FDG accumulation of the gastro-oesophageal junction does not need further investigation if there is no correlate on CT. Of course, in both of our presented cases, there was a mass on CT, justifying further investigation. In both cases, even after multiple biopsies were performed—although not advisable in leiomyomas—malignancy could not be confirmed.

PET-positive leiomyomas of the uterus were already described by Nishizawa et al. [5] were hormonal dependency could be a partial explanation of the FDG uptake in those benign tumours. Approximately 10% of leiomyomas in premenopausal women are PET positive and the level of ¹⁸F- FDG uptake can change in time, but has no correlation with possible malignant degeneration.

In our literature search for PET-positive oesophageal leiomyomas, we found three other cases of isolated PET-positive leiomyomas of the oesophagus [6–8], all located in the lower third of the oesophagus and one case of diffuse leiomyomatosis of the oesophagus and the female genital tract [9]. Higher levels of growth factors and increased activity of smooth muscles were shoved forward as possible explanations for the increased ¹⁸F- FDG uptake. In our presented cases, the immunohistochemical markers typical for leiomyoma: desmin and α-smooth muscle actin were positive. In the first case, the marker CD34, typical for GIST, was also positive. In our second case, the mild ¹⁸F- FDG uptake could possibly be explained by the simultaneous presentation of oesophagitis as suggested earlier in this discussion. Nonetheless, in our first case, the only explanation for the abnormal ¹⁸F- FDG uptake is the tumour itself. Unfortunately, we cannot give the exact standardized uptake value in our two cases because one PET was made in another centre.

The choice of treatment in oesophageal leiomyoma is debateable, and especially in our first case, where the patient is completely asymptomatic, surgical treatment may not be necessary. However, the suspicion of malignancy on PET in the first case and the symptomatic second case justified a surgical treatment. Extramucosal enucleation via thoracotomy is still the most commonly used treatment for oesophageal leiomyoma, although thoracoscopic or laparoscopic procedures are increasingly used with good results [10]. We performed in both cases a left thoracotomy because of suspected malignancy.

CONCLUSION

A leiomyoma of the oesophagus may be a cause of a false-positive PET and could complicate a correct diagnosis between benign and malignant oesophageal lesions. Final decision in the treatment of PET-positive lesions must also be based on morphological imaging such as endoscopy, ultrasonography, CT or MRI. We ask for a high level of caution in these cases to prevent unnecessary surgical procedures.

Conflict of interest: none declared.