Primary Peritoneal Psammocarcinoma Misdiagnosed as an Heterotopic Ossification: A Case Report

A 55-year-old female visited the emergency room with severe right flank pain. She had a history of laparoscopic hysterectomy due to adenomyosis, right ovarian cystectomy, and bilateral salpingectomy performed 4 years ago. Subsequently, she complained of sustained right lower abdominal pain for several years and had undergone contrast-enhanced CT twice during the 2 years of follow-up; however, the findings were unremarkable. During physical examination on this visit, there were pain and tenderness in the right lower abdomen. Laboratory tests showed mildly elevated erythrocyte sedimentation rate (25 mm/h, normal range: 0–20 mm/h) and amylase level (96 U/L, normal range: 0–90 U/L). On plain radiograph examination of the abdomen performed 1 year ago, the findings were unremarkable ( Fig. 1A ). But contrast-enhanced CT of the abdomen done at the same time revealed multiple calcified solid nodules in the right lower abdomen along the great omentum and a calcific mass measuring 5.1 cm × 4.4 cm × 0.7 cm in the pelvic cavity ( Fig. 1B ). Both ovaries appeared to be normal in size and shape. The calcified mass in the pelvic cavity appeared flat (or sheet), as seen on coronal reformatted images, appearing not to have a mass effect ( Fig. 1B ). Because the patient had a history of hysterectomy and both ovaries looked intact, the mass was thought to be heterotopic ossification due to her postoperative status. It was recommended excisional biopsy for pathological diagnosis because heterotopic ossification after pelvic surgery is extremely rare; however, the patient was lost to follow-up. One year later, she underwent another noncontrast CT because of sustained and aggravated lower abdominal pain. A calcified solid mass previously observed in the pelvic cavity showed no interval change, although several new calcific peritoneal nodules developed in left upper abdomen were observed. Laboratory tests for tumor markers revealed a mildly increased cancer antigen-125 (CA-125) level (82.99 U/mL, normal range: 0–35 U/mL). For further evaluation, contrast-enhanced pelvic MRI was performed. On axial T2-weighted imaging, the calcified pelvic mass showed heterogeneous signal intensity and contrast-enhanced T1weighted imaging revealed that calcified solid mass showed subtle enhancement ( Fig. 1C ). Diffusion weighted image and apparent diffusion coefficient (ADC) image showed diffusion restriction only at a given focal area within the pelvic mass ( Fig. 1D ). Diagnostic laparoscopic partial omentectomy led to the diagnosis of serous carcinoma with extensive psammoma bodies. Conversion of laparoscopic to open laparotomy and serial debulking surgery were done. On pathological result, the cross-sectional surface of the specimen were grainy and coarsely granular appearance and it was finally diagnosed primary peritoneal psammocarcinoma ( Fig. 1E ). After surgical resection, the patient was discharged and transferred to the Hematology and Oncology Department for chemotherapy. Written informed consent was obtained from the patient.

Primary peritoneal psammocarcinoma is a rare type of serous carcinoma that can develop in the peritoneum, ovary, and uterus ( 1 2 ). The term of psammocarcinoma was first described by Grimaldi in 1916 ( 3 ) and it can be distinguished from serous carcinoma by its massive formation of psammoma bodies and invasion of adjacent organs. Like a borderline serous tumor, psammocarcinoma has a better prognosis than high-grade serous carcinomas ( 1 ). Here, we report a very rare case of primary peritoneal psammocarcinoma presented on CT and MRI.

Primary peritoneal psammocarcinoma is the rare disease entity including low grade malignant potential, with some characteristics of massive formation of psammoma bodies more than 75% of epithelial cells, invasion of adjacent organ with moderate cytological atypia ( 1 ). Low proliferative activity of Ki67, diploid DNA with BRAF mutation are major features of psammocarcinoma ( 4 ). Psammoma bodies are calcified bodies formed by calcium accumulation in a single necrotic cell or degenerated tumor cells. They are multiple, discrete, and laminated. The radiologic feature of psammocarcinoma is as follows. On CT, serous psammocarcinoma can be identified by extensive pelvic mass calcifications and disseminated peritoneal nodules that were not identified in simple radiography ( 5 ). This suggests that the tumor contains sandy rather than dense calcifications. On enhanced T1-weighted MRI, the calcified pelvic mass shows a sandy and coarsely granular appearance due to scattered signal loss of clustered psammomatous calcifications ( 5 ). By using this modality and radiologic features, the presence of psammomatous calcification could be revealed. The abundant psammomatous calcification and scattered distribution at both primary and disseminated lesions are radiologic feature of this disease entity ( 5 ). Heterotopic ossification, which was misdiagnosed in our case, especially associated with pelvic surgery, is very rare and its pathogenesis is unclear ( 6 ). However, in our case, the first manifestation of a calcified pelvic mass was a sheet-like appearance rather than a mass-forming lesion, the reason it was suggested heterotopic ossification as the first diagnosis. There are several differential diagnoses for the primary peritoneal psammocarcinoma. Ovarian serous carcinoma is the first differential diagnosis. It often contains psammoma bodies in both primary and disseminated peritoneal lesions. However, on CT, these appear as highly condensed and widespread calcifications that differ from psammocarcinomas ( 7 ). Second, primary papillary serous carcinoma of the peritoneum is considered. The CT features of primary papillary serous carcinoma of the peritoneum include nodular peritoneal thickening and omental caking, often causing abundant psammomatous calcifications that have a radiographic appearance similar to that of ovarian serous psammocarcinomas. Although the pelvic peritoneum is more extensively involved and usually forms pelvic masses, the ovaries are intact and only superficially involved in primary papillary serous carcinoma of the peritoneum ( 7 ). The standard treatment for primary peritoneal psammocarcinoma is debulking surgery, followed by a few cycles of adjuvant chemotherapy ( 8 ). However, the therapeutic benefits of postoperative chemotherapy are controversial. Therefore, further trials are required to establish adjuvant chemotherapy. In most cases, patients with primary peritoneal psammocarcinoma present with the disease at an advanced stage; however, the prognosis is relatively favorable ( 9 ). Therefore, preoperative differential diagnosis for primary peritoneal psammocarcinoma will be helpful for patient treatment and prognosis prediction. Primary peritoneal psammocarcinoma is very rare, including psammoma bodies, rendering diagnosis difficult in patients with a history of surgery that could accompany dystrophic calcification. In our case, the surgical history of laparoscopic hysterectomy and the normal appearance of both ovaries led to misdiagnosis. In conclusion, although primary peritoneal psammocarcinoma is very rare, it should be considered a possible differential diagnosis in patients with a normal appearance of both ovaries combined with massive ossification in the pelvic cavity and peritoneal nodules after pelvic surgery.