** Current clinical guideline consensus documentation may be accessed here.
Pseudomyxoma peritonei (PMP) is a rare illness with an incidence rate of around 3.2 persons per million. It is a diagnosis you may only give to one or two patients throughout your career, if at all. It is often difficult to differentiate between PMP and other more common types of mucinous tumour such as ovarian cancer without a thorough histological examination by an experienced pathologist.
Pseudomyxoma is a widely disseminated mucinous neoplasia occurring in the peritoneal cavity, and usually arises from a ruptured appendiceal tumour. It may present as a generalised accumulation of mucin in the abdominal cavity which often causes a distended abdomen, colloquially termed “jelly belly”. The accumulation of fluid becomes a problem for the patient as the pressure from the increasing amount of mucin begins to compress the internal organs, causing intestinal obstruction and pain. Other presentations may include enlarged ovaries in women or a new onset hernia.
Most cases of PMP are slow-growing, and patients generally experience a gradual increase in mucin accumulation over many years. You may find that some patients become symptomatic quite suddenly possibly as a result of intestinal obstruction or, in women, with the development of mucinous ovarian cysts or Krukenberg tumours which can grow rapidly in the space of a few months.
Differential diagnoses to consider include primary mucinous tumours of the colon, pancreas, gall bladder or ovary, and peritoneal mesothelioma. An experienced pathologist will be key to assisting you with obtaining a definitive diagnosis. An important point to note is that true PMP rarely originates in the ovary. Most cases of PMP with a large ovarian “cystadenoma” are found to have a clinically occult appendiceal primary.
Diagnosis of PMP is often first suspected through the use of abdominal imaging which demonstrates features such as mucinous ascites, omental cake and enlarged ovaries. Scalloping of the liver and splenic surfaces is a characteristic finding on CT. Primary tumours of the appendix may also be seen in these images, although this is not always the case. The most common appearance is that of an appendiceal mucocele. Sometimes, PMP is diagnosed during surgical interventions for other conditions.
Definitive diagnosis requires histopathological assessment of the appendiceal primary and the peritoneal disease. The most common lesion found in the appendix is a low grade appendiceal mucinous neoplasm (LAMN). Other possible appendiceal primaries include mucinous adenocarcinoma and the rare high grade appendiceal mucinous neoplasm (HAMN).The PMP is classified pathologically into three major categories: low grade mucinous carcinoma peritonei (previously known as disseminated peritoneal adenomucinosis), high grade mucinous carcinoma peritonei and high grade mucinous carcinoma peritonei with signet ring cells. The category of the disease may affect the treatment given to the patient, so consultation with an experienced pathologist is key to providing the best treatment.
Once diagnosed, the patient may either be treated radically with cytoreductive surgery (CRS) and heated intraperitoneal chemotherapy (HIPEC), or else palliative debulking may be offered to manage symptoms. Sometimes, a wait-and-see approach, where the patient is monitored closely for progression of the disease, is most appropriate. Since it is often a very slow-growing cancer, patients who are frail or have other problems with their health may have a better chance of maintaining their quality of life without surgical intervention.
CRS is an extensive and invasive procedure, but is usually well-tolerated when performed in an experienced centre. The aim is to remove all visible tumour from the abdominal cavity. In addition to stripping peritoneum from the abdominal wall and hemidiaphragms, CRS can include colectomy, splenectomy, omentectomy and cholecystectomy, and, in females, hysterectomy and bilateral salpingo-oophorectomy. CRS is usually combined with hyperthermic intraperitoneal chemotherapy (HIPEC), which involves instilling heated chemotherapy solution into the peritoneal cavity to eliminate any residual circulating tumour cells reducing the risk of recurrence.
Pseudomyxoma peritonei is a “seeding” type cancer, and so extra care must be taken with PMP patients during surgery. If you come across a mucinous tumour or unexpected ascites in a patient during surgery, it is important to consider PMP. You may wish to check the appendix for involvement, and if you locate a tumour there, it is wise to consult with an abdominal cancer specialist immediately. Most importantly, avoid opening more surgical planes if possible. The opening of surgical planes leaves new, uninvolved tissue layers open to potential infiltration by shed PMP tumour cells, making it more difficult for PMP specialist surgeons to provide curative treatment to the patient later.
If you require more detailed information about pseudomyxoma peritonei, a list of consultant surgeons, pathologists and researchers who are willing to assist you in locating information in your country can be found by contacting the EuroPMP representative for your area.
The Christie NHS Foundation Trust has kindly provided their documentation for physicians on the basics of PMP and providing palliative care to patients in the UK. Please note that this information is given for informational purposes only. Please contact your local health authority for more information on PMP treatment and palliation protocols in your country.
The most up to date estimate of prevalence and incidence of Pseudomyxoma peritonei in Europe may be found here.