Integrally calcified solitary fibrous tumor in the retroperitoneum: a case report and review of the literature

Abstract

Solitary fibrous tumor (SFT) is a rare stromal neoplasm and usually occurs in the thoracic cavity. We here report a case of retroperitoneal SFT with prominent calcification. A 64-year-old man presented with an incidentally detected retroperitoneal mass in the right upper abdomen. Imaging tests indicated an integrally calcified mass. The lesion was observed for 2 years and laparoscopically resected according to the patient's wish. Microscopically, the mass was mostly occupied by calcification and proliferous spindle cells were scattered with positive CD34 expression. We diagnosed morphologically benign SFT and the patient remained disease-free 1 year after the excision. There has been no report of such integrally calcified SFT. Retroperitoneal SFT is difficult to make a preoperative diagnosis, and careful follow-up after the excision is recommended because morphological malignancy does not always correspond to clinical malignancy.

Keywords: Calcification; Retroperitoneum; Solitary fibrous tumor.

Fig. 1

Preoperative images. a, b Images of plain computed tomography on the patient’s first visit. A mass with extremely high densities was located next to the undersurface of the right hepatic lobe and the right kidney (yellow arrows). It was 6.5 cm in the longest diameter. c An image of plain computed tomography 2 years after the patient’s first visit (yellow arrow). There were no remarkable changes of the mass in its appearance or size. d, e Magnetic resonance imaging on the patient’s first visit. The mass showed low signal intensities on both d T1- and e T2-weighted images (red arrows)

Fig. 2

A laparoscopic image of the right upper abdomen and photographs of the excised specimen. a In the right upper retroperitoneum, a white and hard mass was observed next to the right hepatic lobe and the right kidney. b The excised specimen presented calcified mass. c Division surface of the specimen presented mainly calcification and partially red soft tissues

Fig. 3

Microscopic findings of the specimen. a An image of hematoxylin-eosin staining. Spindle cells with low cytological atypia densely proliferated in much hyalinizing collagen fiber. b–h Images of immunoreactivity for CD34, Bcl-2, vimentin, SMA, S-100, p53, and Ki-67 are shown, respectively