A strange case of ascites

Clinical History

An otherwise healthy 72 year-old male reported unexplained increase of his abdominal circumference in the last two years. Ultrasound (not shown) showed mild ascites. CEA=42 ng/ml (upper limit=5 ng/ml); CA 15-3=35 U/ml (upper limit=29 U/ml). Gastroscopy and colonoscopy were unremarkable. US-guided paracentesis withdrew few traces of thick, mucinous-like material.

Imaging Findings

CT revealed abnormal abdominal distension given by dense fluid (10-15 HU), consistent with jelly material, and thin enhancing septa (Figure 1, white arrowheads), with the small bowel (Figure 1, black arrowheads) compressed by the jelly mass. In addition, liver and spleen showed surface scalloping (Figure 2).
The whole omentum was removed and gross inspection revealed the presence of multiple areas of necrosis (Figure 3, yellow arrows), associated with a number of cystic, jelly-containing masses (Figure 3, white arrows).
A new CT performed one month after surgery confirmed the successful removal of the whole omentum (Figure 4), excepting a round, hypodense lesion over the liver dome (Figure 5), consistent with a remaining implant of the peritoneal tumor.

Discussion

Clinical, radiological and histological findings well correlate with the diagnosis of pseudomyxoma peritonei (PMP), which is a borderline malignant condition characterized by mucinous peritoneal implants and mucinous ascites, often leading to progressive obliteration of the peritoneal cavity, associated with intestinal obstruction, with a poorly predictable prognosis [1]. PMP is usually caused by the intra-abdominal spread of invasive or non-invasive appendiceal tumours, and occasionally by mucinous tumours at other sites, such as the colon and ovaries [2-4] but sometimes, as in our case, the primary tumour remains unknown.
Ronnett et al. [2] proposed three histological categories of PMP: i) low-grade tumours as disseminated peritoneal adenomucinosis (DPAM), ii) high-grade tumours as peritoneal mucinous carcinomatosis (PMCA), and iii) peritoneal mucinous carcinomatosis with intermediate or discordant features (PMCA-I/D); with a ten-year survival rate of 65-68%, 3-14%, 20-28% respectively.
CT signs of PMP are not specific. There are some signs that should point to the diagnosis. In particular, attention should be paid to the presence of scalloping, which indicates extrinsic compression of the liver and/or spleen by gelatinous masses. Also, loculation of intraperitoneal effusion, curvilinear calcifications, and lesions predominating in the greater omentum and in the diaphragmatic peritoneum can be seen [5, 6]. When PMP is suspected, the examiner should pay high attention to the presence of a fluid or soft-tissue mass on the appendix, which in our case was free of disease.
Treatment of PMP is yet to be firmly established. At present, surgical cytoreduction associated with locoregional chemotherapy (HIPEC) seems to be the best option, as reported by Chua et al. [7].
After surgery our patient was in general good condition and tumour markers returned to normal range. A new CT performed one month after surgery confirmed the successful removal of the whole omentum (Figure 4), except a round, hypodense lesion over the liver dome (Figure 5), consistent with a remaining implant of the peritoneal tumour. The patient is now followed-up and a cycle of hiperthermic intraperitoneal chemotherapy (HIPEC) is currently under discussion.

Differential Diagnosis List

Final Diagnosis

Low-grade mucinous neoplasia.

URL:	https://eurorad.org/case/13042
DOI:	10.1594/EURORAD/CASE.13042
ISSN:	1563-4086