VIPoma overview

# Overview
VIPoma is a rare tumor of the non-beta cells of the pancreas that results in the overproduction of the hormone vasoactive intestinal peptide (VIP). On histopathological analysis, composition of uniform, small to intermediate-sized cells in clusters, nests, and trabecular growth patterns with hyperchromatic nuclei and scant cytoplasm are seen. VIPoma must be differentiated from ganglioneuroblastoma, ganglioneuroma, factitious diarrhea, bile salt enteropathy, rectal vilous adenomas, and laxative abuse. The incidence VIPoma is approximately 0.01 per 100,000 individuals worldwide, and females are more commonly affected than males. If left untreated, patients with VIPoma may progress to develop watery diarrhea, abdominal pain, bloating, nausea, vomiting, skin rash, backache, flushing, and lethargy. Common complications of VIPoma include metastasis, cardiac arrest from low blood potassium level, and dehydration. The presence of metastasis is associated with a particularly poor prognosis, with a 5 year survival rate of 60%. The hallmark of VIPoma is watery diarrhea. A positive history of abdominal pain, weight loss, numbness, and weakness is suggestive of VIPoma. Common physical examination findings of VIPoma include tachycardia, rash, facial flushing, abdominal tenderness, and abdominal distention. Laboratory tests used in the diagnosis of VIPoma include serum vasoactive intestinal polypeptide (VIP) levels, basal gastric acid output, and basic metabolic pannel for potassium, bicarbonate, magnesium, and calcium levels. On CT scan VIPoma is characterized by hypervascularity with diffuse multiple metastatic nodulation. Abdominal MRI is helpful in the diagnosis of VIPoma which is characterized by a mass that is hypointense on T1-weighted and hyperintense on T2-weighted MRI. Initial treatment in patient with VIPoma is prompt replacement of fluid and electrolyte losses, steroids may be used to provide symptomatic relief. Surgery is the mainstay of treatment.

# Historical Perspective
VIPoma which is also known as Verner-Morrison syndrome was first described in 1958 by Verner and Morrison.

# Pathophysiology
A VIPoma is a rare tumor of the non-beta cells of the pancreas that results in the overproduction of the hormone vasoactive intestinal peptide (VIP). On microscopichistopathological analysis, findings of VIPoma are composition of uniform, small to intermediate-sized cells in clusters, nests, and trabecular growth patterns with hyperchromatic nuclei and scant cytoplasm.

# Causes
The cause of VIPoma has not been identified.

# Differentiating VIPoma From Other Diseases
VIPoma must be differentiated from ganglioneuroblastoma, ganglioneuroma, factitious diarrhea, bile salt enteropathy, rectal vilous adenomas, and laxative abuse.

# Epidemiology and Demographics
The annual incidence of VIPoma is approximately 0.01 per 100,000 (approx. 1 in 10 million) individuals worldwide. Female are more commonly affected by VIPoma than male. The incidence of VIPoma increases with age, the median age at diagnosis in adults is 50 years. VIPoma in children is usually diagnosed between age 2 to 4.

# Risk Factors
The most important risk factor in the development of VIPoma is a positive family history of multiple endocrine neoplasia type 1.

# Screening
According to the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for VIPoma.

# Natural History, Complications and Prognosis
If left untreated, patients with VIPoma may progress to develop watery diarrhea, abdominal pain, bloating, nausea, vomiting, skin rash, backache, flushing, and lethargy. Common complications of VIPoma include metastasis, cardiac arrest from low blood potassium level, and dehydration. The presence of metastasis is associated with a particularly poor prognosis among patients with VIPoma, with a 5 year survival rate of 60%.

# Diagnosis

## Diagnostic Study of Choice
The diagnostic study of choice for Vipoma is the measurement of serum vasoactive intestinal polypeptide (VIP) concentration.

## History and Symptoms
The hallmark of Vipoma is watery diarrhea. A positive history of abdominal pain, weight loss, numbness, and weakness is suggestive of VIPoma . The most common symptoms of VIPoma include watery diarrhea like cholera, dehydration, lethargy, muscle weakness, weight loss, numbness, and flushing.

## Physical Examination
Common physical examination findings of VIPoma include tachycardia, rash, facial flushing, abdominal tenderness, muscle weakness, and abdominal distention.

## Laboratory Findings
Laboratory tests used in the diagnosis of VIPoma include serum vasoactive intestinal polypeptide (VIP) levels, basal gastric acid output, and CMP for potassium, bicarbonate, magnesium, and calcium levels.

## Electrocardiogram
There are no ECG findings associated with VIPoma.

## X-ray
There are no x-ray findings associated with VIPoma.

## CT
On CT scan VIPoma is characterized by hypervascularity with diffuse multiple metastatic nodulation. CT scan are highly accurate for tumor localization of primary neuroendocrine pancreatic tumor. Since most of them are more than 3cm in size at the time of presentation. Sensitivity of contrast enhanced CT for VIPoma approaches 100%.

## MRI
Abdominal MRI is helpful in the diagnosis of VIPoma. On abdominal MRI, VIPoma is characterized by a mass which is hypointense on T1-weighted MRI and hyperintense on T2-weighted MRI.

## Echocardiography or Ultrasound
Endoscopic ultrasound may be helpful in the diagnosis of VIPoma. Finding on ultrasound suggestive of VIPoma is hypoechoic tumor in the distal part of pancreas.

## Other Imaging Findings
Other imaging studies for VIPoma include somatostatin receptor scintigraphy and PET scan using radiolabeled somatostatin analogs.

## Other Diagnostic Studies
Other diagnostic studies for VIPoma include immunohistochemical staining test, which demonstrates staining for markers such as chromogranin A, cytokeratin 19, synaptophysin, Ki-67, neuron specific enolase, PGP 9.5.

# Treatment

## Medical Therapy
Initial treatment in patient with VIPoma is prompt replacement of fluid and correction of electrolyte imbalance and acid-base disturbance. Somatostatin analogues like short acting octreotide is useful for controlling diarrhea by blocking the release of VIP. Octreotide is later replaced by longer acting depot preparation of somatostatin analogues like sandostatin or lanreotide.

## Interventions
The mainstay of treatment for VIPoma is surgery.  Hepatic artery embolization or transcatheter chemoembolization with doxorubicin or cisplatin is usually reserved for patients with liver metastases. Moreover, in patients with liver metastases less than 3 cm radiofrequency ablation and cryoablation can be used.

## Surgery
Surgery is the mainstay of treatment for VIPoma. Surgery should be considered after initial symptomatic management of VIPoma inoperable cases. Complete surgical resection of the tumor is the only curative treatment for VIPoma. If the tumor cannot be removed completely, surgical debulking may have palliative effect for control of hormonal symptoms.

## Primary Prevention
There are no established measures for the primary prevention of VIPoma.

## Secondary Prevention
Effective measures for the secondary prevention of VIPoma include history and physical examination, serum VIP levels and indicated markers, and multi-phasic CT scan or MRI.