EP311 - A Case of a Solitary Fibrous Tumor in a Young Female presenting a Retrorectal Mass

Purpose/Background: Solitary fibrous tumors are rare mesenchymal neoplasms. In this paper, we report a case of a young female who initially developed of pain on the hip and constipation. Succeeding imaging and examination showed a bulky presacral mass with solid and hypervascular components located at the anterior coccyx. This mass was resected enbloc with the colon and rectum. Histopathologic specimen results showed spindle cell neoplasm resembling a solitary fibrous tumor. Requested immunohistochemistry were done STAT6, CD34, CD117 and DOG 1 all consistent as a solitary fibrous tumor

Methods/Interventions: This case was initially diagnosed as a case of coccygeal angiosarcoma from an another institution. Patient underwent pelvic exploration, partial tumor excision last 2011. The procedure was abandoned after heavy bleeding was encountered. Biopsy of the tumor revealed angiosarcoma. No further treatment was done.
On initial consult, the patient was complaining of constipation and decreasing stool caliber. There was no hematochezia or abdominal pain. On T2-weighted MRI, a 9.18 x 9.07 cm fairly defined, heterogenous mass in the retrorectal region with adherence to the internal iliac vessels and surrounding tributaries and causing rightward displacement and compression of the rectum. There were no enlarged lymph nodes. There were no apparent metastatic lesions on computed tomography scan.
The patient underwent preoperative cystoscopy, with bilateral ureteral stenting. A midline laparotomy incision was then performed. A total hysterectomy was performed to allow for better exposure of the operative field. As the dissection was developed, numerous tributaries from both left and right internal iliac vessels were encountered. As the tumor was adherent to the posterior rectum, an extended Hartmann’s procedure was performed, with the distal line of resection at the bare rectal cuff. A decision to not anastomose the bowel ends was due to poor nutritional status and the conduct of an extensive multivisceral resection

Results/Outcomes: We incurred at total of 3500 cc estimated blood loss for the nine-hour procedure. The patient was discharged well on postoperative day 10, having needed additional days in the hospital of intravenous antibiotics for urinary tract infection.
Histopathologic specimen results showed spindle cell neoplasm. Immunohistochemistry studies STAT6,CD117, and DOG 1 were consistent and confirmed the diagnosis of an SFT

Conclusion/Discussion: Retrorectal solitary fibrous tumors are rare neoplasms. There are no large case series that exist. SFTs only comprised less than 2% of all soft tissue tumors. As of 2022, the database of US National Cancer Institute showed that of 804 patients with SFT, only 16 cases were reported to have originated from the sacrum or presacrum.
A feature of these tumors is the difficulty in detecting them early because the mass tends to grow deep in the pelvic cavity precluding any clinical symptoms. Most cases are locally-advanced at the time of diagnosis, and may already involve adjacent structures.
Some of the reported cases were shown to be malignant and were treated with chemotherapy and or radiotherapy after resection. SFTs can recur and metastasize, thus close surveillance on imaging during follow up is advised. With regards to histopathologic confirmation, the utility of STAT6 immunostaining has proven to be valuable in narrowing a pathological diagnosis. Finally, a multidisciplinary team consensus and preoperative planning is essential in reaching a consolidated treatment plan.

SFT MRI representative cut
On T2 MRI showing a 9.18 x 9.07 cm fairly defined, heterogenous mass in pelvis/presacral region with prominent internal and surrounding vessels causing rightward displacement and compression of rectum. No enlarged lymph nodes.

Enbloc specimen resected
showed a 12x12cm coccygeal mass with multiple neovascularization from the internal iliac vessels. Mass is adherent also to the posterior rectum. The liver is smooth. No carcinomatosis or ascites.