Cystsmayariseatanylevelofthenephron,fromtubulestocollectingducts,andthereforetheyhaveavariable,oftenatrophic,lining.Occasionally,Bowman’scapsulesareinvolvedinthecystformation,andinthesecasesglomerulartuftsmaybeseenwithinthecysticspace.Thepressureoftheexpandingcystsleadstoischemicatrophyoftheinterveningrenalsubstance.Somenormalparenchymamaybedispersedamongthecysts.Evidenceofsuperimposedhypertensionorinfectioniscommon.Asymptomaticlivercystsalsooccurinone-thirdofpatients.
Polycystic kidney disease in adults usually does not produce symptoms until the fourth decade of life, by which time the kidneys are quite large. The most common presenting complaint is flank pain or a heavy, dragging sensation. Acute distention of a cyst, either by intracystic hemorrhage or by obstruction, may cause excruciating pain. Sometimes attention is first drawn to the lesion on palpation of an abdominal mass. Intermittent gross hematuria commonly occurs. The most important complications, because of their deleterious effect on already marginal renal function, are hypertension and urinary infection. Hypertension of variable severity develops in about 75% of individuals with this http://ebooksmedicine.net
Fig. 14.22 Autosomaldominantadultpolycystickidney,viewedfromtheexternalsurface(A)andbisected(B).Thekidneyismarkedlyenlarged(centimeter ruleisshownforscale),withnumerousdilatedcysts.
disorder. Saccular aneurysms of the circle of Willis (Chapter 23) are present in 10% to 30% of patients and are associated with a high incidence of subarachnoid hemorrhage.
Although the disease is ultimately fatal, the outlook is generally more favorable than with most chronic kidney diseases. The condition progresses very slowly. End-stage renal disease occurs at about 50 years of age, but there is wide variation in the course, and nearly normal life spans are reported. Patients in whom the disease progresses to renal failure are treated by renal transplantation. Death usually results from uremia or hypertensive complications.
The childhood form of polycystic kidney disease is a rare autosomal recessive disorder that is genetically distinct from adult polycystic kidney disease. It occurs in approximately 1 in 20,000 live births. Perinatal, neonatal, infantile, and juvenile subcategories have been defined, depending on age at presentation and the presence of associated hepatic lesions. All types result from mutations in the PKHD1 gene, coding for a putative membrane receptor protein called fibrocystin. Fibrocystin is found in cilia in tubular epithelial cells, but its function remains unknown.
MORPHOLOGYInautosomalrecessivepolycystickidneydisease,numerous small cysts inthecortexandmedullagivethekidneyasponge-likeappearance.Dilated,elongatedchannelsatrightanglestothecorticalsurfacecompletelyreplacethemedullaandcortex.Thecystshaveauniformliningofcuboidalcells,reflectingtheiroriginfromthecollectingtubules.Thediseaseisinvariablybilateral.Inalmostallcases,findingsincludemultipleepithelium-linedliver cysts andproliferationofportalbileducts.
Perinatal and neonatal forms are most common; serious manifestations usually are present at birth, and young infants may die quickly from hepatic or renal failure. Patients who survive infancy develop liver cirrhosis (congenital hepatic fibrosis).