Fig.20.37 ).Asageneralruletheyaresmall,averaging1to2cmindiameter.Onmicroscopicexamination,adenomasarecomposedofcellssimilartothosepopulatingthenormaladrenalcortex.Aswithotherendocrinetumors,pleomorphismmaybeencounteredinbenigntumorsandisnotareliablemarkerofmalignancy.
Adrenocorticalcarcinomasarerareneoplasmsthatmayoccuratanyage,includinginchildhood.TworareinheritedcausesofadrenalcorticalcarcinomasareLi-Fraumenisyndrome(Chapter6)andBeckwith-Wiedemannsyndrome(Chapter7).Inmostcases,adrenocorticalcarcinomasarelarge,invasivelesionsthateffacethenativeadrenalgland.Oncutsurface,adrenocorticalcarcinomastypicallyarevariegated,poorlydemarcatedlesionscontainingareasof necrosis,hemorrhage,andcysticchange(Fig.
20.42 ).Microscopicexaminationtypicallyshowsthesetumorstobecomposedofwell-differentiatedcellsresemblingthoseseenincorticaladenomasorbizarre,pleomorphiccells,whichmaybedifficulttodistinguishfromthoseofanundifferentiatedcarcinomametastatictotheadrenalgland(
Fig.20.43 ).Adrenalcancershaveastrongtendencytoinvadetheadrenalvein,venacava,andlymphatics.Metastasestoregionalandperiaorticnodesarecommon,asisdistanthematogenousspreadtothelungsandotherviscera.Bonemetastasesareunusual.Themedianpatientsurvivalisabout2years.Ofnote,carcinomasmetastatictotheadrenalcortexaresignificantlymorefrequentthanaprimaryadrenocorticalcarcinoma.
Fig.20.42Adrenalcarcinoma.Thetumordwarfsthekidneyandcom-pressestheupperpole.Itislargelyhemorrhagicandnecrotic.
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The adrenal medulla is embryologically, functionally, and structurally distinct from the adrenal cortex. It is populated by cells derived from the neural crest (chromaffin cells) and their supporting (sustentacular) cells. The chromaffin cells are so named because of their brown-black color after exposure to potassium dichromate. They synthesize and secrete catecholamines in response to signals from preganglionic nerve fibers in the sympathetic nervous system. Similar collections of cells are distributed throughout the body in the extraadrenal paraganglion system. The most important diseases of the adrenal medulla are neoplasms, which include both neuronal neoplasms (including neuroblastomas and more mature ganglion cell tumors) and neoplasms composed of chromaffin cells (pheochromocytomas).
Pheochromocytomas are neoplasms composed of chromaffin cells, which, like their nonneoplastic counterparts, synthesize and release catecholamines and, in some cases, other peptide hormones. These tumors are of special importance because, although uncommon, they (like aldosterone-secreting adenomas) give rise to a surgically correctable form of hypertension.
Pheochromocytomas usually subscribe to a convenient “rule of 10s”: 10% of pheochromocytomas are extraadrenal, occurring in sites such as the organ of Zuckerkandl and the carotid body, where they usually are called paragangliomas, rather than pheochromocytomas.
10% of adrenal pheochromocytomas are bilateral; this proportion may rise to 50% in cases that are associated with familial syndromes.
10% of adrenal pheochromocytomas are malignant, although the associated hypertension represents a serious and potentially lethal complication of even benign tumors.