Unusual Cause of Acute Renal Failure in Pregnancy: Ruptured Renal Artery Aneurysm
A 30-year-old pregnant Hispanic woman with no significant medical history presented to the emergency department with a sudden onset of generalized abdominal pain at 39+ weeks? gestation. Her prenatal visit the day before was unremarkable. Her first pregnancy was uneventful, and her current pregnancy was uncomplicated until now. On arrival, her blood pressure was 88/40 mm Hg and heart rate, 136 beats/min. Physical examination revealed somnolence and generalized abdominal tenderness, without guarding. Fetal heart rate was initially 50 to 60 beats/min but soon became undetectable. Laboratory results showed: hemoglobin, 10.2 g/dL; blood urea nitrogen, 15 mg/dL; and creatinine, 1.2 mg/dL.
Despite aggressive resuscitation with fluids and multiple blood transfusions, the patient developed hypovolemic shock. Her hemoglobin concentration decreased to 8.7 g/dL in less than 2 hours. She was taken to the operating room with a presumptive diagnosis of hemorrhagic shock secondary to abruptio placentae. Emergency cesarean section was performed, and an expanding left iliac retroperitoneal hematoma of unclear origin was noted. Surgical exploration revealed a ruptured left renal artery aneurysm requiring left nephrectomy. There was no evidence of splenic artery aneurysm or rupture.
The patient?s postoperative course was complicated by hypotension requiring treatment with vasopressors and blood products, acute respiratory distress syndrome, and nonoliguric acute renal failure. Her serum creatinine concentration peaked to 7.0 mg/dL on hospital day 6 (Figure 1) and subsequently improved without the need for dialysis, paralleling the patient?s recovery from respiratory failure and shock. She received a total of 24 units of packed red blood cells, 16 units of fresh frozen plasma, 2 units of platelets, and 20 units of cryoglobulins during her hospital stay.
On hospital day 24 the patient was discharged home. At follow-up 2 weeks later, she was normotensive, and her serum creatinine level had returned to baseline (1.2 mg/dL).
Renal artery aneurysms account for about 1% of all aneurysms. Although the true incidence is unknown, estimates range from 0.01% to 0.09%, based on autopsy series, and from 0.9% to 2.5%, based on angiographic studies.1 Risk factors for aneurysm rupture include size more than 1.5-cm diameter, lack of calcification, pregnancy, and uncontrolled blood pressure.2
To date, 29 cases of renal artery aneurysm rupture during pregnancy have been reported in the English medical literature since the first case was described by Chisolm in 1926.3 To our knowledge, only 1 other case of acute renal failure caused by ruptured renal artery aneurysm has been reported.4 Our case represents the second such report and the 30th case of renal artery aneurysm during pregnancy.
Renal artery aneurysms may be caused by congenital defects in the elastic tissue of the media or the internal elastic lamina of the intima; inflammatory changes; atherosclerosis; fibromuscular dysplasia; and, in rare instances, trauma.3 Spontaneous intra-abdominal hemorrhage from ruptured aneurysms during pregnancy is uncommon. Ruptured splenic artery aneurysms account for the majority of cases, although bleeding from aortic, iliac, ovarian, and renal arteries has also been described.3 Rupture of renal artery aneurysms is extremely rare. Of the 30 known cases, 21 were reported in the past 25 years.
The increased risk of renal artery aneurysm rupture during pregnancy has been attributed to the associated hemodynamic and hormonal changes. Rupture may be secondary to the greater cardiac output and intravascular volume, which may increase renal artery blood flow.5 Most ruptures of renal artery aneurysms occur in the third trimester, when the gravid uterus increases intra-abdominal pressure and compresses the aorta and inferior vena cava, possibly causing significant changes in blood pressure and the distribution of blood flow. This, in turn, may induce structural changes in the arteries that predispose to aneurysm rupture.3
Increased intra-abdominal pressure, however, does not completely explain the increased risk of rupture during pregnancy, since no cases during labor, when intra-abdominal pressure peaks, have been reported in the English medical literature. Moreover, 2 of the cases occurred postpartum,1 which has led some experts to speculate that pregnancy-related hormonal changes may cause disruption and duplication of the internal elastic lamina and medial fibroplasia, with accumulation of acid mucopolysaccharides, thus increasing the risk of aneurysmal rupture.6
The clinical characteristics and outcomes of the 30 reported cases are listed in the Table. Although maternal age does not appear to play a role, renal artery aneurysm rupture is more common in multigravid than in primigravid women. Bilateral involvement was evident in only 3 cases.5,7,8 The left renal artery was more frequently affected than the right (17 versus 9 cases, respectively) in pregnant women, whereas the right artery was more often involved in nonpregnant women and in men.9 There was no lateralization of aneurysm in the 4 reported cases of women with congenital solitary kidneys.4,8,10
Since 1970 the rate of maternal mortality has decreased dramatically, from 89% to about 10%, despite the lack of improvement in our ability to diagnose renal artery aneurysms before they rupture. The declining death rate probably reflects advances in the medical care of critically ill patients. Fetal survival has improved from 0% to 53% during the same period. Of patients who have survived such a catastrophic event, the majority underwent nephrectomies to control retroperitoneal bleeding. In the past 2 decades, however, ruptured renal artery aneurysm repair with kidney salvage has become increasingly common. Embolization of the renal artery successfully controlled retroperitoneal bleeding in 1 case, although the patient subsequently died from a ruptured splenic artery aneursym.11
In all the reported cases, including ours, the aneurysm was not diagnosed until rupture, because most patients are asymptomatic before the event. Patients with ruptured renal artery aneurysm typically present with sudden onset of severe flank, abdominal, or back pain followed by shock.5 Some patients present with hypertension, microscopic or macroscopic hematuria, a localized bruit in the epigastric region, or a palpable mass suggestive of the aneurysm.4,5,11 Unless the physician is keenly aware of this possibility, the diagnosis of ruptured renal artery aneurysm may be missed, because the clinical picture can be easily confused with abruptio placentae, uterine rupture, twisted ovarian cyst, ectopic pregnancy, pyelonephritis, or nephrolithiasis.3
If a renal artery aneurysm is diagnosed before rupture in a pregnant patient, surgery is mandatory.11 Detection of retroperitoneal hematoma by renal ultrasound or computed tomography in a patient presenting with abdominal pain may aid in the diagnosis of a rupture. In hemodynamically stable patients, renal arteriography is used to assess arterial anatomy and function of the contralateral kidney before surgery.4 In a patient presenting with shock, however, the diagnosis may only be made intraoperatively. Of patients who have survived aneurysmal rupture, 74% presented with shock, and 50% lost the fetus.
Despite the often catastrophic presentation, only 1 other case of acute renal failure has been described in a case series of pregnant women.4 Our patient developed nonoliguric acute renal failure secondary to acute tubular necrosis (Figure 2) with serum creatinine peaking at 7.0 mg/dL. In these 2 cases, spontaneous improvement of renal function occurred without the need for dialysis. Acute renal failure may have been averted in some cases by prompt and aggressive resuscitation of hemodynamically unstable patients; alternatively, it may have occurred but was not reported.
Although uncommon, physicians should consider the diagnosis of renal artery aneurysm in a pregnant woman who presents with abdominal pain and hypotension. When such an aneurysm is diagnosed, it is important to look carefully for other aneurysms, since 20% to 30% of renal artery aneurysms are bilateral, and approximately 2.5% to 30% of them involve extrarenal aneurysms.4,6
Renal artery aneurysm rupture during pregnancy is a rare but catastrophic event that should be considered in a pregnant woman presenting with hypotension and abdominal pain. Early diagnosis and timely intervention are critical. Aggressive hemodynamic support with colloids and blood products should be given as needed to maintain blood pressure and avoid ischemic injury. Attempts should be made to salvage the affected kidney, verify the presence of the contralateral kidney, and identify vascular anomalies of the unaffected kidney for long-term patient and renal survival.
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