assessment of UPJO.CT with arterial and venous

Based on current existing literature, it is difficult

phase contrast­enhanced images has 97% sensi­

to draw conclusions regarding the relation of

tivity and 92% specificity in the detection of a

hypertension to UPJO or PUV.74

lower pole crossing vessel.69 The symmetry of

parenchymal opacification can serve as a surro­

gate marker of renal function.70 In the last sev­

Postobstructive Diuresis

eral years, techniques such as small section

multidetector row CT and multiplanar reforma­

Postobstructive diuresis is a significant loss of

tion allow for excellent 3D reconstruction of

water and possibly solute that can occur after

UPJ anatomy.70

relief of urinary obstruction. It is usually arbi­

trarily defined as a persistent urine output great

Magnetic Resonance Urography

than 200 mL/h.77­79Most commonly, this occurs

after relief of BUO (or UUO in a solitary kid­

Magnetic resonance (MR) urography is an

ney), but it has been reported after relief of UUO

evolving group of technique that allows for opti­

with a normal contralateral kidney.80 Post­

mal visualization of many urinary tract abnor­

obstructive diuresis can be severe enough to

malities without the use of ionizing radiation.71

cause life­threatening dehydration and electro­

It can be performed in two ways: static­fluid MR

lyte disorders.

urography (T2­weighted MR urography) and

Several physiological

derangements have

excretory MR urography (T1­weighted MR

been discovered to occur in postobstructive

urography). Static­fluid MR urography is well

diuresis.Investigatorshaveidentifiedadecreased

suited for patients with dilated collecting sys­

expression of aquaporin genes and proteins

tems because it is dependent on the presence of

with BUO.81,82 Having a decreased number of

urine in the collecting systems and not on renal

aquaporin channels in the collecting tubules

function.71 In excretory MR urography, a gado­

impairs renal reabsorption of water and con­

linium­based contrast agent is administered and

tributes to ongoing diuresis. Ureteral obstruc­

the collecting system is imaged. A low dose of

tion has also been demonstrated to decrease the

furosemide given 2 min prior to contrast injec­

activity of Na+K+­ATPase that contributes to

tion is typically administered during excretory

postobstructive diuresis and naturalis.83 Rec­

MR urography.72 Utilizing excretory MR urogra­

ently, Norregaard et al. have demonstrated that

phy, Karabacakoglu et al. reported 92.8% accu­

cyclooxygenase­2 activity

transiently contrib­

racy for diagnosing stone disease and 100%

uted to increased water and sodium excretion

accuracy at diagnosing other causes of obstruc­

after release of ureteral obstruction.84 They

tive uropathy.72 The technique of MR urography

reported that treatment of rats with COX­2

is becoming more widely available, especially

inhibitor parecoxib decreased the downregula­

because imaging processing software is now

tion of aquaporin channels with BUO.

available in the public domain.73

Patients more likely to experience significant

postobstructive diuresis have preexisting vol­

ume overload, severe renal impairment, or cen­

Hypertension

tral nervous system manifestations.77 Mana­

gement initially includes urethral catheter place­

Hypertension is rarely a consequence of congen­

ment. In the setting of urinary retention, there is

ital UPJ obstruction. In a literature review,

no benefit to gradual bladder decompression.79

Farnham et al. only identified 15 cases of hyper­

Serum electrolytes and urine osmolarity should

tension attributed to UPJ obstruction from

be monitored at least every 12 h. In a clinically

1960–2005.74 One series followed 71 adults with

stable patient, oral fluid replacement alone is

UPJO an average of 17 years and found only four

recommended as excessive intravenous fluids

patients developed hypertension.75 Parkhouse

may prolong the period of diuresis.66 It has also

et al. reviewed a series of 88 boys with posterior

been suggested that fluid replacement be two­

urethral valves (PUV) followed for 11–22 years

thirds of the fluid output.77 Unstable patients are

afterdiagnosis.76 Duringthattime,sevenpatients

best monitored in a critical care setting with

developed hypertension. However, other pos­

specific fluid replacement dictated by serum

sible causes of hypertension were not reported.

electrolytes.