Pseudomyxoma peritonei refers to the intraperitoneal accumulation of a gelatinous ascites secondary to rupture of a mucinous tumour. The most common cause is a ruptured mucinous tumour of the appendix/appendiceal mucocoele 10.
Occasionally, mucinous tumours of the colon, rectum, stomach, pancreas and urachal tumours 9-10,13 are implicated. There is some ongoing contention as to whether primary ovarian tumours are a frequent source in their own right, or whether in these cases the appendix is the primary site and the ovarian lesion is metastatic 2-3.
The remarkable feature of pseudomyxoma peritonei is that this neoplastic, progressive process often arises from a seemingly benign or well differentiated primary tumour 3. With the rupture of these mucinous tumours, the mucus and cells will flow along with the peritoneal fluid and spread with deposits commonly seen at the pelvis, paracolic gutters, on the liver capsule, and on the omentum 13.
Pseudomyxoma peritonei may be divided into two pathological subtypes which have aetiological and prognostic significance 4:
- a peritoneal neoplasm composed largely of mucin associated with fibrosis with minimal cytologic atypia and mitoses
- the primary tumour is generally an adenoma
peritoneal mucinous carcinoma
- characterised by proliferative epithelium, glands, nests, or individual cells with marked cytologic atypia
- the primary is a mucinous adenocarcinoma
Not all cases fit neatly into these categories, and many patients have intermediate or discordant features.
However, a long term follow-up study 4 of 109 patients found 5-year survival rates were markedly different: 75% for the adenomucinosis group and 14% for the mucinous carcinoma group. The intermediate/discordant group 5 year survival was 50%.
It is typically characterised by loculated collections of fluid causing scalloping of abdominopelvic organs.
May show evidence of ascites with centrally displaced small bowel loops and scattered punctate or curvilinear calcifications.
- echogenic peritoneal masses or ascites with echogenic particles which (unlike other forms of particulate ascites such as haemoperitoneum or pus in the peritoneum) do not move 6
- the small bowel loops displaced medially.
- may show scalloping of the liver, spleen and at times other organs
- low attenuation, often loculated fluid throughout the peritoneum, omentum and mesentery.
- scalloping of visceral surfaces, particularly the liver 5
- scattered (curvilinear or punctate) calcifications may be frequently present 5
- tends to remain localised to the peritoneal cavity
MRI has been shown with increased accuracy in detecting peritoneal metastatic disease compared to CT 13. Reported signal characteristics of the collections include 8:
- T1: typically low signal
- T2: typically high signal
- T1 C+ (Gd): may show enhancement 12
- DWI: solid peritoneal and serosal implants show restricted diffusion 13
Fluorine-18 fluorodeoxyglucose (FDG) PET-CT has a low sensitivity for peritoneal implants 13.
Treatment and prognosis
This is a progressive and often fatal disease. Recurrent bowel obstructions are commonly due to the fibrosis and adhesions in advanced disease 13.
Treatment is surgical debulking, followed by infusion of intraperitoneal chemotherapy. Aggressive surgical treatment has been considered based on the calculation of the peritoneal cancer index (PCI), which is a prognostic indicator based on the amount of tumour found at laparoscopy. This index has alternatively been performed using CT or MRI 13.
General imaging differential considerations include:
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