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pheochromocytoma

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pheochromocytoma
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{{short description|Type of neuroendocrine tumor}}







factoids
Pheochromocytomas (PH or PCC) are tumors arising from chromaffin cells of the adrenal medulla that synthesize, store, metabolize and usually but not always secrete catecholamines. Extra-adrenal paragangliomas (often described as extra-adrenal pheochromocytomas) are closely related, though less common, tumors that originate in the ganglia of the sympathetic nervous system and are named based upon the primary anatomical site of origin. The term is from the Greek phaios (dark), chroma (color), kytos (cell), and -oma (tumor).

Signs and symptoms

The signs and symptoms of a pheochromocytoma are those of sympathetic nervous system hyperactivity,WEB,weblink Pheochromocytoma: Symptoms, Treatment, Diagnosis, Test, medicinenet.com, 4 May 2018, no,weblink" title="web.archive.org/web/20170716113907weblink">weblink 16 July 2017, including: A pheochromocytoma can also cause resistant arterial hypertension. A pheochromocytoma can be fatal if it causes a hypertensive emergency, that is, severely high blood pressure that impairs one or more organ systems (formerly called "malignant hypertension"). This hypertension is not well controlled with standard blood pressure medications.Not all patients experience all of the signs and symptoms listed. The most common presentation is headache, excessive sweating, and increased heart rate, with the attack subsiding in less than one hour.Tumors may grow large, but most are smaller than {{convert|10|cm|0}}.Pheochromocytoma crisis is a rare and potentially lifethreatening emergency. It can occur spontaneously or be precipitated by administration of pharmacological agents, tumor manipulation, micturition (urinary bladder pheochromocytoma), or foods that aggravate release of catecholamines by the tumor.doi: 10.4158/EP10388.CR.{{PMID|21324811}}

Complications

The massive release of catecholamines in pheochromocytoma can cause damage to heart cells.{{Harvnb|Goldman|2011|pp=327}} This damage may be due to either compromising the coronary microcirculation or by direct toxic effects on the heart cells.A common clinical presentation of pheochromocytoma includes hypertension, due to increased total peripheral resistance. Most pheochromocytomas secrete norepinephrine, which is a vasoconstrictor via α-adrenergic receptor stimulation, however research has yet to significantly correlate the increase in peripheral resistance with increased circulating norepinephrine. Theories behind the inability to correlate the two variables include simultaneous dopamine release, which has the opposing effect of norepinephrine in terms of vasodilation. Other mechanisms propose the down-regulation of α-adrenergic receptors or the release of other hormones that have opposing effects to norepinephrine. Due to increased catecholamine production, cardiovascular complications upon presentation and throughout the course of the disease are common. Complications that arise from these cardiovascular disturbances include blood pressure changes as well as possible sudden death, heart attack despite no prior history, noncardiogenic pulmonary shock/edema, and arrhythmias.Pheochromocytoma is also capable of causing, at presentation, pseudo-obstruction of bowels, diabetic ketoacidosis, or multisystem crisis involving lactic acidosis. These symptoms may be in part due to the co-secretion of other hormones associated with norepinephrine, such as corticotropin-releasing hormone, adrenocorticotropin, and interleukin six.Pheochromocytoma may go undiagnosed or undetected for multiple reasons. The main reason is the fact that the tumors are rare. Hypertension may not clinically present itself right away due to the fact that catecholamines can convert into their biologically inactive forms in the tumor, suppressing symptoms. Lastly, the symptoms of the disease are non-specific and common to stress neuronal release of catecholamines. Lag in diagnosis averages about three years. Presymptomatic diagnosis is most possible in patients with germ-line inheritance.

Cause

The hereditary implications of pheochromocytoma are still being investigated, however, genes have been identified as genomic biomarkers to aid in the identification of inherited disease. [1] Of these genes studied, the most well-known include VHL, RET, and NF1. Aberrations of these genes are associated with bilateral disease.The RET protein is a tyrosine kinase receptor that plays an integral role in development of sympathetic neurons [2]. Mutations in the gene via germ-line (MEN-2) or somatic acquisition activate multiple signaling pathways involved in PCC, as well as other neuroendocrine tumors in humans. MEN-2 generally results from a gain-of-function variant of this RET gene, and MEN-2 is commonly associated with pheochromocytoma and amyloid producing medullary thyroid carcinoma.Mutations in two subunits of the succinate dehydrogenase gene, SDHB and SDHD, have been strongly associated with cancer presenting at a younger age as well as extra-adrenal location, multiple tumors/metastasis, and poor prognosis.Pheochromocytoma linked to MEN II can be caused by RET oncogene mutations. Both syndromes are characterized by pheochromocytoma as well as thyroid cancer (thyroid medullary carcinoma). MEN IIA also presents with hyperparathyroidism, while MEN IIB also presents with mucosal neuroma.

Diagnosis

(File:Adrenal pheochromocytoma (3) histopathology.jpg|thumb|150px|Histopathology of adrenal pheochromocytoma. Adrenectomy specimen.)File:Pheochromocytoma Scan.jpg|thumb|Pheochromocytoma (dark circular shadow near body center) localized by MIBG scintigraphy. Front and back views also show radioiodineradioiodine(File:Pheochromocytoma 2 0001.jpg|thumb|pheochromocytoma on ultrasound)The diagnosis can be established by measuring catecholamines and metanephrines in plasma (blood) or through a 24-hour urine collection. Care should be taken to rule out other causes of adrenergic (adrenaline-like) excess like hypoglycemia, stress, exercise, and drugs affecting the catecholamines like stimulants, methyldopa, dopamine agonists, or ganglion blocking antihypertensives. Various foodstuffs (e.g. coffee, tea, bananas, chocolate, cocoa, citrus fruits, and vanilla) can also affect the levels of urinary metanephrine and VMA (vanillylmandelic acid).WEB,weblink Catecholamines – urine – Penn State Hershey Medical Center, Pennstatehershey.adam.com, 2011-01-06, 2013-02-23, no,weblink" title="web.archive.org/web/20131203023424weblink">weblink 2013-12-03, Imaging by computed tomography or a T2 weighted MRI of the head, neck, and chest, and abdomen can help localize the tumor. Tumors can also be located using an MIBG scan, which is scintigraphy using iodine-123-marked metaiodobenzylguanidine. Even finer localization can be obtained in certain PET scan centers using PET-CT or PET-MRI with [18F] fluorodopamineJOURNAL, 6-[18F]Fluorodopamine Positron Emission Tomographic (PET) Scanning for Diagnostic Localization of Pheochromocytoma, Hypertension, 38, 1, 6–8, Hyper.ahajournals.org, July 2001, 10.1161/01.HYP.38.1.6, or FDOPA.6-L-18F-fluorodihydroxyphenylalanine PET in neuroendocrine tumors: basic aspects and emerging clinical applications, Journal of Nuclear Medicine 2008, 49, 573-586. DOI: 10.2967/jnumed.107.045708Pheochromocytomas occur most often during young-adult to mid-adult life.These tumors can form a pattern with other endocrine gland cancers which is labeled multiple endocrine neoplasia (MEN). Pheochromocytoma may occur in patients with MEN 2 and MEN 3 (MEN 2B). Von Hippel Lindau patients may also develop these tumors.{{Harvnb|Goldman|2011|pp=185}}Patients experiencing symptoms associated with pheochromocytoma should be aware that it is rare. However, it often goes undiagnosed until autopsy; therefore patients might wisely choose to take steps to provide a physician with important clues, such as recording whether blood pressure changes significantly during episodes of apparent anxiety.

Testing

Testing prior to tumor excision helps ascertain whether the tumor is a singular tumor or if there are multiple, if it is ectopic or adrenal originating, malignant or benign, and isolated or present with other tumors in context of inherited disease. CT is the most commonly used imaging technique, however MRI is preferred. MIBG scanning should be used when possible, as it is the most accurate way to locate cancer in catecholamine producing cancers, as catecholamine plasma membrane and vesicular transport systems are especially abundant in pheochromocytoma cells. Imaging using MIBG would yield specific and sensitive results compared to CT and MRI, as the latter two are non-specific generalized imaging techniquesFile:Adrenaline.svg|thumb|150px|EpinephrineEpinephrineFile:Noradrenaline2.svg|thumb|150px|NorepinephrineNorepinephrine
  • Blood tests: Buters and others have suggested that analysis of free metanephrines (metadrenalines) (normetanephrine and metanephrine) in blood plasma is the most accurate test for detecting pheochromocytoma.
  • Urine tests: Although this test is slightly less effective than plasma testing it is still considered highly effective in diagnosis. Usually the metabolites of norepinephrine and epinephrine, normetanephrine (NMN) and metanephrine (MN), are found in relatively small amounts in normal humans. The increased excretion of these metabolites is indicative of the disease, but does not completely rule out other diseases which may cause the same excretion values.
  • Other Tests:


*One diagnostic test used in the past for a pheochromocytoma is to administer clonidine, a centrally-acting alpha-2 agonist used to treat high blood pressure. Clonidine mimics catecholamines in the brain, causing it to reduce the activity of the sympathetic nerves controlling the adrenal medulla. A healthy adrenal medulla will respond to the clonidine suppression test by reducing catecholamine production; the lack of a response is evidence of pheochromocytoma.
*Chromogranin A is elevated in case of pheochromocytoma.JOURNAL, 15850005, 2005, Cotesta, D, Caliumi, C, Alò, P, Petramala, L, Reale, MG, Masciangelo, R, Signore, A, Cianci, R, D'erasmo, E, Letizia, C, High plasma levels of human chromogranin A and adrenomedullin in patients with pheochromocytoma, 91, 1, 53–8, Tumori, 8,
File:Adrenal pheochromocytoma (1) histopathology.jpg|Micrograph of pheochromocytoma.File:Adrenal pheochromocytoma (2) histopathology.jpg|Micrograph of pheochromocytoma.File:Adrenal pheochromocytoma (3) histopathology.jpg|Micrograph of pheochromocytoma.File:Bilateral pheo MEN2.jpg|Bilateral pheochromocytoma in MEN2.File:Pheochromocytoma.jpg|Pheochromocytoma. CT abdomen.File:Pheochromocytoma2.jpg|Pheochromocytoma. CT abdomen.

Tumor location

In adults, approximately 80% of pheochromocytomas are unilateral and solitary, 10% are bilateral, and 10% are extra-adrenal. In children, a quarter of tumors are bilateral, and an additional quarter are extra-adrenal. Solitary lesions inexplicably favor the right side. Although pheochromocytomas may grow to large size (>3 kg), most weigh

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