An 87-years old woman with left lower abdominal pain was referred to our hospital with suspicion of a malignant ovarian tumour. She had suffered from non-tuberculous mycobacterial lung disease treated with multiple antibiotics. She also had a history of glaucoma and osteoporosis. Laboratory data showed slight anaemia and elevated tumour markers; Serum levels of CA125, CA19-9, and CEA were 176.3 U/ml, 63.5 U/ml, and 7.4ng/ml, respectively.
Non-contrast CT obtained at the referred hospital showed a large intrapelvic mass with a part with dense calcification. A small number of ascites was also seen, although any peritoneal implants, lymph nodes, or distant metastasis was not found. T2-weighted images revealed a multilocular cystic mass with a solid part with a very low signal. The signals of cyst contents were slightly variable on both T1- and T2-weighted images. The solid portion was only weakly enhanced after the administration of contrast media. However, the septa at the ventral part of the cystic mass were thick and showed hyperintense on T2-weighted images and strong enhancement. The septa also showed restricted diffusion on diffusion-weighted images. As the uterus was displaced right anterolaterally, the mass was suspected as a left ovarian tumour, although any proper ovarian tissue was detected.
Brenner tumour is an ovarian epithelial tumour composed of transitional cells. Nearly all are benign counterparts, composed of nests of bland transitional/urothelial epithelium set within a dense fibromatous stroma . On the other hand, the borderline Brenner tumour is defined as a tumour of transitional/urothelial epithelium displaying papillary architecture and lacking stromal invasion . They are rare and often appear as large cystic masses. It has been reported that tumours containing both Brenner and mucinous components are more common. Such “mixed Brenner-mucinous tumours” may resemble ovarian mucinous neoplasms or borderline Brenner tumours . Therefore, there is confusion among the imaging findings of benign, borderline Brenner tumours and primary mucinous neoplasms.
Benign Brenner tumours are often incidentally found for their microscopic size. On the other hand, borderline Brenner tumours are larger, and pelvic mass or abdominal distention is the typical clinical presentation. They affect older women, whose mean age is in their seventh decade .
The benign Brenner tumour imaging findings are characterized by dense fibrous stroma surrounding transitional cell nests; It shows very low signal intensity on T2-weighted images as low as skeletal muscles . Calcification is commonly seen . However, they can appear as stained glass-type multilocular cystic masses resembling primary mucinous neoplasms as metaplastic mucinous component form the dominant part of the tumour [4, 5]. On the other hand, Borderline mucinous tumours usually appear as a multilocular cystic mass, and a benign Brenner component is typically present with a more solid and fibrous cut surface . Therefore, diagnosing benign and borderline or malignant Brenner tumours with preoperative imaging is challenging. Takahama et al. reported that a borderline Brenner tumour appeared to be a cystic lesion with papillary projection . Oh et al. reported that the signal intensity of solid components on T2-weighted images was as low as muscle in benign and hyperintense in borderline and malignant. MR findings of the present case were similar to a “mixed Brenner-mucinous tumour,” although the borderline component appeared thick septa with high signal on T2-weighted images and restricted diffusion.
Most cases are diagnosed at stage I and cured by surgery; recurrence is rare [2, 9].
Take Home Message / Teaching Points
Benign Brenner tumour often appears as a multilocular cystic mass with a solid component showing a low signal on T2-weighted images. However, if hyperintense foci or any part of restricted diffusion are observed, a borderline counterpart should be considered.
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