Unusual glomus tumor of the bladder: a rare case report and literature review

Background Glomus tumor (GT), which are neoplasms of the glomus body, usually occur in the extremities, particularly under the nail bed. GT occurring in the bladder is very rare and has been reported as sporadic. In the present study, a rare case of bladder GT is reported and its clinical and histopathological characteristics are summarized by literature review. Case presentation A 57-year-old woman presented with intermittent gross hematuria for 2 years. Urinalysis displayed hematuria. The bladder ultrasound showed an avascular and homogeneous isoechoic polypoid mass with a maximum diameter of 6 mm at the right lateral wall of bladder. The bladder endoscopic examination showed a polypoid lesion, with a smooth surface, located in the right lateral wall. Then, a transurethral resection was performed, its histopathological features indicated a benign GT. Conclusions GT arising in the bladder is extremely rare, and only four cases have been identified in studies reported in English. It is difficult to diagnose bladder GTs according to their clinical features. The gold standard method used for their diagnosis is histopathology. However, it should also be considered in the differential diagnosis for bladder mass.


Introduction
Glomus tumor (GT) is a mesenchymal neoplasm, composed of a mixture of glomus cells, blood vessels and smooth muscle cells arising from the glomus body. GT can occur in almost any part of the body, but it is most commonly seen in the extremities, particularly in the nail bed [1]. GT occurring in the bladder is very rare and has been reported sporadically. To the best of our knowledge, only 4 cases of bladder GT have been previously identified in studies reported in English [2][3][4][5]. The present study aimed to (1) present an extremely rare case of GT in the bladder and (2) summarize its clinical and histopathologic features by literature review.

Case presentation
A 57-year-old woman presented with intermittent gross hematuria for 2 years. She did not report any other symptoms. Physical examination indicated no abnormal findings. Blood cell counts and biochemical tests were within the reference range. Urinalysis displayed hematuria. Therefore, it was suggested that she should undergo a urinary system ultrasound examination. The kidney and ureter ultrasounds indicated no abnormal findings, whereas the bladder ultrasound revealed an avascular and homogeneous isoechoic polypoid mass with a maximum diameter of 6 mm at the right lateral wall of the bladder (Fig. 1). She has no bladder tumors history or family history. So, the bladder of the patient was examined endoscopically and a polypoid lesion (6 mm in maximum diameter) was noted with a smooth surface, located in the right lateral wall (Fig. 2). Subsequently, a transurethral resection (TUR) was performed and the lesion was easily removed. Microscopic

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*Correspondence: wangjiwei167@163.com 1 Department of Ultrasound, The Second Affiliated Hospital of Nanchang University, Nanchang 330006, Jiangxi, China Full list of author information is available at the end of the article examination indicated that the neoplasm was well circumscribed and composed of nests of monomorphic cells with bland nuclei and eosinophilic cytoplasm, clustered around dilated vessels. Atypia, mitoses, intravascular growth and necrosis were absent (Fig. 3). Immunohistochemical staining revealed that the neoplastic cells reacted positively to the smooth muscle actin (SMA) and vimentin, whereas they were negative to desmin (Fig. 4). A diagnosis of benign bladder GT was made. The patient remained asymptomatic and no recurrence was observed within a 2-year follow up.
GT occurring in the bladder is very rare and has been reported as sporadic. To the best of our knowledge, only 4 cases of human bladder GT have been identified in the literature, indicating that the current case is the fifth. The clinical data of these five patients are presented in Table 1 and the histopathological data in Table 2. After reviewing of the clinical features of these patients, the following conclusions were made: (1) Bladder GT can occur in males (M) and females (F), no significant gender difference was evident; (2) Bladder GT mostly occurred in elderly subjects, with an age range from 56 to 84 years; (3) Bladder GT patients presented with hematuria or were asymptomatic; (4) Bladder GT patients usually exhibited no history of bladder tumor; (5) The size and location of bladder GT were flexible (the size ranged from 3 to 65 mm and the location could be anterior, lateral, or posterolateral wall); (6) Although the majority of GTs are benign, the bladder GTs were described in the present and previous studies were not always benign (2/5 cases were benign, 2/5 cases were atypical and 1/5 case was malignant); (7) Transurethral resection is the most common treatment used for benign or atypical bladder GT, whereas for malignant bladder GT, comprehensive treatment could be performed according to patient condition. Although these findings are meaningful, no specific clinical feature was noted. The pathological and immunohistochemical examination are the standard methods used in the diagnosis of bladder GT.
GT is composed of a mixture of glomus cells, blood vessels and smooth muscle cells. GT is usually benign and rarely malignant or atypical. The criteria of malignancy GT are the following: (1) tumor with a deep location, (2) a size more than 2 cm, (3) atypical mitotic figures or apparent nuclear atypia, (4) 5 or more mitotic figures/50 highpower field [24]. The atypical GT was defined as a tumor with a high-grade nuclear pleomorphism in the absence of any other malignant features, such as large size, deep location, infiltrative growth, mitotic activity, or necrosis. The majority of the GTs are benign, whereas this not commonly noted for bladder GT. According to the present literature review, more than half of the patients with bladder GT were malignant or atypical cases.
In conclusion, GT arising in the bladder is extremely rare, and only four cases have been identified in studies reported in English. It is difficult to diagnose bladder GTs according to their clinical features. The gold standard method used for their diagnosis is histopathology. However, it should also be considered in the differential diagnosis for bladder mass.