We report a unique case of axillary schwannoma mimicking lymph node metastasis. Furthermore, the present case highlighted the difficulty in making an accurate diagnosis of tumors in the axillary region and the importance of histopathological examination.

A great concern when examining patients with tumors in the axillary region with breast or other cancers is whether the tumor is lymph node metastasis or not. In particular, there are several problems when distinguishing schwannomas from lymph node metastasis. First, the two tumors resemble each other in imaging findings [4,5,6,7,8]. Schwannoma in the axillary region is very similar to swollen lymph nodes on CT [4] and has a low T1 signal and high T2 signal on MRI, as does lymph node metastasis [8]. In the present case, lymph node metastasis was initially suspected based on imaging findings. In addition, fluorodeoxyglucose (FDG)-positron emission tomography is a powerful modality for detecting malignant tumors, but FDG accumulation has also been observed in schwannomas [5, 9]. Therefore, distinguishing between schwannoma and lymph node metastasis by imaging studies alone is impractical. Second, cytology by FNA or CNB for tumors in the axillary region is often technically difficult because of anatomical problems; tumors in the axillary region are generally in contact with the axillary vasculature or nerves. There is a risk of iatrogenic vascular or nerve injury at the time of puncture. Therefore, some patients require an excisional biopsy to obtain an accurate diagnosis [5, 7, 8].

Tinel’s sign is a finding that is explained as a radiating pain caused by tapping over the affected nerve. This finding is characteristic of axillary schwannoma, and described in previous reports [7, 10]. In the present case, the patient also felt radiating pain on palpation. Furthermore, she felt a sharp and radiating pain when FNA and CNB were being performed. This sharp pain, felt during the tumor biopsy by FNA or CNB, is an invaluable finding suggesting that the tumor originates from the nervous system [7]. This finding can play a key role in diagnosing axillary schwannoma.

Making an accurate diagnosis of tumors in the axillary region is often difficult as mentioned above. However, clinicians should always make an effort to distinguish between lymph node metastasis and other tumors by histopathological examination, because the treatment strategies are completely different. Axillary schwannoma is a very rare tumor, but its clinical presentation and imaging findings generally mimic lymph node metastasis. When examining patients with a history of malignancy, especially breast cancer, and tumors in the axillary region, clinicians should consider the possibility of schwannoma and avoid chemotherapy or radiation therapy on the assumption that they have lymph node metastasis, without histopathological examinations.

In conclusion, axillary schwannomas often mimic lymph node metastasis in patients with a history of malignancy, particularly breast cancer. To select the optimal treatment, the clinicians should make as accurately as possible a diagnosis, with histopathological examinations, when examining patients with cancer who develop tumors in the axillary region.