Spinal extradural solitary fibrous tumor with retiform and papillary features

We report a 66-year-old man with a spinal, extradural solitary fibrous tumor showing unique retiform and papillary architecture. The patient presented in May 2008 with worsening right-sided lower back pain and urinary frequency. Magnetic resonance imaging of the spine documented a heterogeneously enhancing dumbbell-shaped extradural lesion causing cord compression at T11/12 level. The tumor extended to the paravertebral soft tissue and invaded the right adjacent vertebral pedicles and laminae. An angiogram showed prominent vascular supply mainly from the right T11 radicular artery. The patient underwent surgery to relieve cord compression in May 2008 and a second operation following embolization with coils in October 2009. No recurrence was observed at the last neuroimaging follow-up in June 2012. The tumor was composed of vimentin, CD34, Bcl-2, and CD99-positive rounded or slightly elongated cells with scant cytoplasm and oval to spindle nuclei. Several pseudovascular spaces reminiscent of the rete testis were present, and several of them contained papillary projections. Cytologic atypia was minimal, and mitotic activity was low. Focal infiltration of the paraspinal adipose tissue was seen at microscopic level. To our knowledge, retiform and papillary features have never been reported in a solitary fibrous tumor.