A 42-year-old woman revealed that, during childhood, a soft tissue mass near the anus was found. The mass was about 4 cm x 5 cm in size, with a slightly tough texture, and she did not experience pain; thus, she received no special attention. In 2019, she felt an obvious pain in the lump and went to the hospital for local lumpectomy. After surgery, a deep sinus was found, and the doctor repeatedly irrigated the lump with normal saline. After 7 months, she again felt pain in the buttocks and experienced difficulty in urination and defecation. She was readmitted to the hospital, and the computed tomography (CT) scan showed a mass in the pelvis. Vaginal puncture and drainage guided by B ultrasound was performed to relieve difficulty in defecation. Sacrococcygeal cyst excision was performed 10 days later, and postoperative pathology showed epidermoid cyst. The pain in the buttocks continued to recur after the patient was discharged from the hospital. After that, puncture and drainage were performed five times under the guidance of B ultrasound. The last time a drainage tube was placed in the tumor, about 25 ml of yellowish clear liquid was drawn out every day. Later, the patient went to our hospital for treatment.
Pelvic magnetic resonance imaging (MRI) showed multiple abnormal signal shadows in the presacral and sacrococcygeal regions, some of which were considered abscesses. MRI scans showed a multiloculated T1 hypointense and T2 hyperintense cystic lesion in the right buttock tissue and sacrococcygeal region. Annular enhancement of the cystic wall was observed on the T2-weighted gadolinium-enhanced MRI scans ( Figure 1 ). Colonoscopy showed no obvious abnormality. The admission laboratory examination showed that the levels of tumor serum markers, such as CEA, CA199, AFP, and CA724, were the scope of the standard. Also, there were no signs of infection. Surgical resection was performed again, and a mass of about 4 cm x 3 cm was removed ( Figure 2 ). Unfortunately, the tumor could not be completely removed.
The final histological diagnosis was EC with locally moderately differentiated adenocarcinoma ( Figure 3 ). Outside the cyst wall is fibrous connective tissue and smooth muscle ( Figures 3A, B ). The specimen showed benign cyst lesions covered by a single layer of columnar or cuboidal epithelium. Some of the cyst walls were lined by dysplastic epithelium, with interstitial infiltration. Local cancerous lesions showed glands of different sizes and disorderly arrangement ( Figures 3C, D ). Immunohistochemical staining of SATB2 and CDX2 in the cyst epithelial cells showed strong nuclear staining ( Figures 2E, F ). In addition, MLH1, MSH2, MSH6, PMS2, CDH-17, and CK20 and other specific molecules were also positive, and CK7 was negative. All the above immunohistochemical results showed the same immune characteristics as intestinal adenocarcinoma.
Four months later, the patient's symptoms of swelling and pain recurred. Considering the recurrence of the lesion, the patient was given a radiation dose of 60 Gy/25F. For the rare disease, there is insufficient evidence on the role of adjuvant chemotherapy. Given the immunohistochemical results, a fluorinated pyrimidine- and oxaliplatin-containing regimen was recommended, but the patient declined chemotherapy. We plan to identify KRAS, NRAS, and BRAF mutations and evaluate MSI status to guide subsequent individualized therapeutic and oncological prognosis for the patient, which failed due to the patient's financial reasons. As of 20 July 2022, the patient had a good outcome, and a recently repeated MRI scan did not show any evidence of cyst recurrence. This indicates that radiotherapy shows a good local control effect.