Renal Forniceal Rupture in the Setting of Obstructing Ureteral Stones: An Analysis of Stone Characterization and Urologic Intervention Pattern

Abstract

Introduction and Objective:

Forniceal rupture due to obstructing ureterolithiasis (FROU) is a seldom encountered radiographic finding, but the impact of this diagnosis and influence on stone management has not been well studied in the literature. The purpose of the study is to examine stone characteristics and intervention patterns of patients with radiographic evidence of FROU.

Materials and Methods:

A retrospective analysis of all patients with radiographic evidence of FROU was compared with patients with obstructing ureteral stones without forniceal ruptures (noFROU). All patients presented to our Emergency Department from January 2015 until December 2018. Data analyzed included patient demographics, clinical presentation, stone characteristics, and management pattern. Primary outcome was need for hospital admission and surgical intervention.

Results:

Thirty-two patients with FROU (mean age = 45) were compared with 50 patients with noFROU (mean age = 57). Univariate analysis revealed that age, history of diabetes mellitus, history of hypertension, days of symptoms, degree of hydronephrosis, and degree of perinephric stranding were associated with forniceal rupture (p ≤ 0.05). On multivariate analysis, only degree of perinephric stranding remained significant (p ≤ 0.05). Average maximum axial stone diameter in the FROU group was 5.1 mm vs 4.7 mm in the noFROU group (p = 0.66). Overall, 68.8% of stones were located within the distal ureter in the FROU group vs 48.8% in the noFROU group (p = 0.09). There was no difference in hospital admission (FROU 37.5% vs noFROU 44%, p = 0.56) and need for surgical intervention (FROU 50% vs noFROU 48%, p = 0.86). There were no 30-day complications in patients with FROU.

Conclusions:

Ureteral stone location and size does not seem to impact the presence of FROU. FROU may be an alarming reported finding but its presence does not appear to impact clinical outcomes or affect urological management, including admission or need for urologic intervention.

Introduction

Renal forniceal rupture is a rare finding that involves urinary extravasation into the perirenal space from downstream obstruction. Most commonly, forniceal rupture is due to obstructing ureterolithiasis (FROU), however it can arise from any obstructive etiology of the urinary tract^1

–6—a proposed mechanism for FROU involves sudden occlusion of the ureter by a small calculus; this overwhelms its compensatory mechanisms to reduce pressure in the collecting system, leading to rupture at the weakest location. Patients typically present with acute flank and pelvic pain and other symptoms associated with renal colic. It is hypothesized that as the fornix ruptures and urine extravasates into the perirenal space, the release of pressure leads to a resolution of pain sometimes described as a “self-help” mechanism.⁷ Forniceal ruptures are seldom problematic but this process has been associated with morbidities, including perinephric abscesses and urosepsis.⁸ There is a lack of consensus to guide the management of FROU and yet due to the threat of such morbid conditions, some urologists favor endourological intervention.¹

Forniceal rupture is a radiographic diagnosis, often detected on cross-sectional imaging in the appropriate clinical context. Objective radiographic evidence of forniceal rupture requires visualization of contrast media extravasation into the perirenal space.⁸ However, in most cases, contrast-enhanced imaging is not performed, and the diagnosis is often a subjective assessment by the radiologist. Studies have cited the use of serial ultrasonography and color duplex sonographic evaluation for both diagnosis and staging of forniceal rupture.⁹ However, these techniques are operator dependent and lack the high sensitivity and specificity of CT urography.¹⁰

The impact of the diagnosis of FROU and its influence on stone management has not been well studied in the literature. The purpose of the study is to examine stone characteristics in the setting of forniceal rupture and to describe intervention patterns of patients with radiographic evidence of FROU.

Materials and Methods

After obtaining approval from the Institutional Review Board, a retrospective review was performed on all patients (>18 years of age) with radiographic evidence of FROU who presented to our tertiary care center's Emergency Department from January 2015 until December 2018. Patients were identified by using queries of our hospital's radiological dictation system (MModal Fluency Discovery) for any cross-sectional abdominopelvic imaging with findings of “forniceal rupture” and “caliceal rupture.” A single radiologist reviewed all CT scans and coded severity of hydronephrosis and degree of perinephric extravasation as a result of forniceal ruptures. This cohort was then compared with a prospectively maintained database of 50 control patients with obstructing ureteral stones without forniceal rupture (noFROU) who consecutively presented to the Emergency Department during that same period.

Data analyzed included patient baseline characteristics, clinical presentation, laboratory results including serum and urine studies, radiographic variables, stone characteristics, management pattern, and interventional outcomes including need for admission and/or surgical intervention.

The severity of perinephric extravasation secondary to forniceal rupture was classified as none, mild, moderate, and severe as based on a previously established criteria.^11,12 The degree of hydronephrosis was graded by a certified radiologist as mild, moderate, and severe based on standard categorizations. The locations of ureteral stones were characterized at the ureteropelvic junction (UPJ), proximal ureter, mid-ureter, and distal ureter. The proximal ureter was defined as the portion of ureter from the UPJ to the sacroiliac (SI) joint, the mid-ureter coursed over the SI joint, and the distal portion included the segment from the caudal edge of the SI joint to the ureterovesical junction.¹³ Creatinine (Cr) before diagnosis was measured as the last serum measurement of Cr available for review before presentation with obstructing ureteral stones. A positive urine culture was defined as growth of greater than 100,000 colony forming units (CFU)/mL of a single organism, or growth of greater than 10,000 CFU/mL of an organism if the patient was symptomatic. Patients with recent endoscopic ureteral intervention (within the past 6 weeks), previous renal surgery or ablative therapy, and non-obstructing renal stones were excluded.

Statistical analysis was performed utilizing SPSS version 26 (IBM). Continuous variables were analyzed by using a two-sample t-test and reported as mean and standard deviation (SD) when following a normal distribution. Categorical data were analyzed by using the Pearson chi-square analysis. Logistic regression analysis was utilized to evaluate the relationship between various patient variables and the presence of forniceal rupture with obstructing ureterolithiasis. A p-value of ≤0.05 was considered statistically significant for all analyses. The primary interventional outcome of our study was the need for hospital admission and surgical intervention.

Results

In total, 32 patients with CT evidence of FROU were compared with a cohort of 50 patients without FROU. Baseline patient characteristics are presented in Table 1. Mean patient age was 57.0 (SD 13.1) years in the FROU group vs 45.1 (SD 13.6) years in the noFROU group (p = 0.01). Patients in the FROU group presented with fewer days of symptoms compared with the noFROU group (1.61 vs 3.44, respectively, p = 0.05). Patients in the FROU group had a higher incidence of diabetes mellitus (DM) compared with those in the noFROU group (25% vs 8%, respectively, p = 0.03). Similarly, history of hypertension had a higher incidence within the FROU group compared with the noFROU group (50% vs 24%, respectively, p = 0.01).

Table 1.

Patient Demographics and Characteristics

	Overall sample	noFROU	FROU	Sig.(p)^*
No. of patients	82	50	32
Age, mean (SD)		45.1 (13.6)	57.0 (13.1)	0.01
BMI, mean (SD)		31.3 (8.4)	29.8 (6.9)	0.43
Days of symptoms, mean (SD)		3.44 (5.0)	1.61 (1.4)	0.05
Gender, n (%)				0.35
Male	36 (43.9)	24 (48.0)	12 (37)
Female	46 (56.1)	26 (52.0)	20 (63)
Diabetes mellitus, n (%)				0.03
No	70 (85.4)	46 (92.0)	24 (75.0)
Yes	12 (14.6)	4 (8.0)	8 (25.0)
History of nephrolithiasis, n (%)				0.12
No	40 (48.8)	21 (42.0)	19 (59.4)
Yes	42 (51.2)	29 (58.0)	13 (40.6)
History of ureteroscopy or ureteral stent placement, n (%)				0.4
No	64 (79.0)	41 (82.0)	23 (74.2)
Yes	17 (21.0)	9 (18.0)	8 (25.8)
Hypertension, n (%)				0.01
No	54 (65.9)	38 (76.0)	16 (50.0)
Yes	28 (34.1)	12 (24.0)	16 (50.0)
History of prior surgery, n (%)				0.54
No	25 (30.5)	14 (28.0)	11 (34.4)
Yes	57 (6.5)	36 (72.0)	21 (65.6)

Bold indicates p value ≤ 0.05.

p-value for statistical analysis.

BMI = body mass index; FROU = forniceal rupture due to obstructing ureterolithiasis; noFROU = obstructing ureteral stones without forniceal rupture; SD = standard deviation.

Radiographic and laboratory findings can be seen in Tables 2 and 3. Mean axial stone diameter (FROU 5.1 mm vs noFROU 4.7 mm, p = 0.7), mean coronal diameter (FROU 5.3 mm vs noFROU 4.8 mm, p = 0.27), and mean axial/coronal proportion (FROU 0.93 vs noFROU 0.86, p = 0.21) were not statistically significant between the two groups.

Table 2.

Stone and Imaging Findings

	Overall sample	noFROU	FROU	Sig.(p)^*
Stone laterality, n (%)				0.89
Left	52 (63.4)	32 (64.0)	20 (62.5)
Right	30 (36.6)	18 (36.0)	12 (37.5)
Axial diameter, mean		4.7 mm	5.1 mm	0.7
Coronal diameter, mean		5.8 mm	5.3 mm	0.27
Axial/coronal proportion, mean		0.86	0.93	0.21
Stone location, n (%)				0.28
Ureteropelvic junction	10 (12.2)	8 (16.0)	2 (6.3)
Proximal ureter	19 (23.2)	13 (26.0)	6 (18.8)
Mid-ureter	7 (8.5)	5 (10.0)	2 (6.3)
Distal ureter	46 (56.1)	24 (48.0)	22 (68.8)
Stone location, n (%)				0.09
Distal	46 (56.1)	24 (48.0)	22 (68.8)
Proximal	36 (43.9)	26 (52.0)	10 (31.2)
Degree of perinephric stranding, n (%)				0.01
None	27 (32.9)	27 (54.0)	0 (0)
Mild	14 (17.1)	11 (22.0)	3 (9.4)
Moderate	18 (22.0)	8 (16.0)	10 (31.3)
Severe	23 (28.0)	4 (8.00)	19 (59.4)
Degree of hydronephrosis, n (%)
Mild	45 (54.9)	33 (66.0)	12 (37.5)	0.02
Moderate	33 (40.2)	16 (32.0)	17 (53.1)
Severe	4 (4.90)	1 (2.00)	3 (9.40)

Bold indicates p value ≤ 0.05.

p-value for statistical analysis.

Table 3.

Lab Values

	Overall sample	noFROU	FROU	Sig.(p)^*
Cr, mean (n, SD)	n = 82	1.38 (50, 2.56)	1.54 (32, 1.85)	0.92
Cr before diagnosis, mean (n, SD)	n = 55	1.31 (32, 2.60)	1.59 (23, 3.23)	0.73
Cr/Cr before diagnosis, mean (n, SD)	n = 55	1.20 (32, 0.21)	1.27 (23, 0.45)	0.49
Serum WBC count, mean (n, SD)	n = 82	11.0 (50, 4.05)	12.7 (32, 6.62)	0.15
Bacteremia, n (%)				0.21
No bacteremia	81 (98.8)	50 (100.0)	31 (96.9)
Bacteremia	1 (1.2)	0 (0)	1 (3.1)
Urinalysis RBC range, n (%)				0.02
0–5	22 (28.9)	13 (27.7)	9 (31.0)
6–25	27 (35.5)	12 (25.5)	15 (51.7)
>25	27 (35.5)	22 (46.8)	5 (17.2)
Urinalysis WBC range, n (%)				0.88
0–5	49 (65.3)	31 (66.0)	18 (64.3
>5	26 (34.7)	16 (34.0)	10 (35.7)
Protein present				0.07
No	39 (48.8)	20 (40.8)	19 (61.3)
Yes	41 (51.3)	29 (59.2)	12 (38.7)
Urine culture				0.17
No growth	63 (76.9)	41 (82.0)	22 (68.8)
Growth	19 (23.1)	9 (18.0)	10 (31.2)

Bold indicates p value ≤ 0.05.

p-value for statistical analysis.

Cr = creatinine; RBC = red blood cell; WBC = white blood cell.

Within the FROU group, 2 (6.3%) patients had UPJ stones, 6 (18.8%) had stones in the proximal ureter, 2 (6.3%) had mid-ureteral stones, and 22 (68.8%) had distal ureteral stones. Similarly, the noFROU group contained 8 (16%) patients with UPJ stones, 13 (26%) patients with proximal ureter stones, 5 (10%) patients with mid-ureteral stones, and 24 (48%) patients with distal stones. When comparing the FROU and the noFROU group, the location of stones on cross-sectional imaging was not statistically significant (p = 0.28). When categorizing stones into a dichotomous format (distal vs proximal), stone location remained statistically insignificant when comparing FROU and noFROU cohorts (p = 0.09). Both the degree of hydronephrosis and degree of perinephric stranding were statistically significant between the FROU and noFROU groups (p = 0.02 and p = 0.01, respectively). There was no statistically significant difference between initial Cr at diagnosis and change in Cr between cohorts (p = 0.92 and p = 0.83, respectively). Positive urine culture was present in 10/32 (31.3%) patients with FROU compared with 9 out of 50 (18%) of those in the noFROU cohort (p = 0.17). On multivariate analysis, only degree of perinephric stranding remained significant (p < 0.05).

There was no difference in hospital admission when comparing those within the FROU and noFROU cohorts (p = 0.56). In addition, there was also no difference in the percentage who underwent urologic intervention between groups (p = 0.86) (Table 4). Indications for intervention included infection, symptomatic control, declining renal function, and stone burden. Out of the 10 patients with infection in the FROU group, 8 had either immediate ureteral stent or nephrostomy tube placement. Two patients had positive cultures, which resulted after discharge on medical expulsive therapy from the Emergency Department. Both patients had spontaneously passed the stone within 3 days from discharge. Some patients had multiple indications for intervention, as detailed in Table 5.

Table 4.

Admission and Intervention

	Overall sample	noFROU	FROU	Sig.(p)^*
Follow-up imaging, n (%)				0.08
No imaging	43 (52.4)	30 (60.0)	13 (40.6)
Imaging	39 (47.6)	20 (40.0)	19 (59.4)
Intervention, n (%)				0.86
No intervention	42 (51.2)	26 (52.0)	16 (50.0)
Intervention	40 (48.8)	24 (48.0)	16 (50.0)
Admissions, n (%)				0.56
No	48 (58.5)	28 (56.0)	20 (62.5)
Yes	34 (41.5)	22 (44.0)	12 (37.5)
Complications, n (%)				0.42
No	80 (97.6)	49 (98.0)	32 (100)
Yes	2 (2.4)	1 (2.0)	0 (0)

p-value for statistical analysis.

Table 5.

Intervention Details

	Overall sample	noFROU	FROU
Immediate ureteroscopy	21	15	6
Indication for intervention
Infection		0	0
Symptomatic control		13	4
Impaired renal function		1	2
Stone burden		5	1
Immediate stent placement with intervention	12	6	6
Indication for intervention
Infection		4	4
Symptomatic control		4	4
Impaired renal function		0	0
Stone burden		1	0
Percutaneous nephrostomy tube placement	7	3	4
Indication for intervention
Infection		3	4
Symptomatic control		0	1
Impaired renal function		0	1
Stone burden		3	4

Discussion

The renal fornix has been described as the most susceptible location of the urinary collecting system to rupture with urinary obstruction.¹⁴ A majority of forniceal ruptures are associated with obstructing ureteral stones.¹ Other associated etiologies of urinary obstruction have also been described, including pelvic malignancy, UPJ obstruction, bladder outlet obstruction, trauma, and iatrogenic causes.^2

–6 Forniceal rupture may be a concerning radiographic finding to the radiologist or emergency medicine physician, which raises the urgency for a urology consultation. Although rare and alarming, there is limited literature on the evaluation of FROU and whether its presence should be an indication for intervention. This study is the first series comparing a cohort of obstructing ureterolithiasis resulting in forniceal ruptures with a cohort of noFROUs.

Presentation

In our study, we find that patients with FROU present with a significantly fewer days of symptoms compared with patients with noFROU (1.6 days vs 3.44 days, p < 0.05), suggesting that the rupturing of the fornix acts as a pop-off mechanism that clinically manifests as an alleviation of renal colic. Regarding the timeline of forniceal rupture, we hypothesize that the rupture occurs within hours of an acutely obstructing ureteral stone. The triphasic pattern of acute urinary obstruction has been well studied in animal models.¹⁵ This model implies that forniceal ruptures occur during the second stage of obstruction, which occurs 2 to 5 hours after an acute obstruction when a decreased glomerular filtration rate (GFR) stimulates a release of vasodilators that increase the renal blood flow.^16,17 If the fornix ruptures at the moment of the highest ureteral pressure, the pop-off mechanism should provide symptomatic relief as well as protective reduction of intrarenal pressure before the reduction of renal blood flow, and consequently the GFR. This is supported by the fact that the change in mean Cr at the time of diagnosis compared with the mean value before diagnosis was −0.05, with the maximum rise in Cr being +0.76 in the FROU group.

Patient characteristics

Patients within the FROU cohort tended to be older than the noFROU control (mean age 57.0 vs 45.1, p = 0.01), which is similar to other studies.^1,8 Patients with FROU also tended to have more comorbidities with higher incidence of hypertension (50% vs 24%, p = 0.01) and DM (25% vs 8%, p = 0.03) when compared with the noFROU group. Diabetes, hypertension, and advanced age are well-known risk factors for chronic kidney disease (CKD). Studies have shown that CKD is associated with fibrosis of the renal parenchyma on histology and may be linked with decreased kidney elasticity.^18,19 It is possible that the diminished renal compliance associated with these risk factors may translate to higher intrarenal pressures and increased likelihood of fornix rupture. Despite this, age, history of hypertension, and history of diabetes did not remain significant on multivariate analysis. Patients within both cohorts had elevated mean serum Cr levels before diagnosis, but estimated GFR and history of CKD was not included into data analysis.

Stone characteristics

Stones within the FROU group tended to be small with a mean axial diameter 5.1 mm, which in the absence of refractory pain, renal failure, or infection lends itself to medical expulsive therapy. This was not statistically different (p = 0.66) from the size of stones within the noFROU control (mean axial diameter 4.7 mm). In the study by Gershman et al., the average diameter of stones causing forniceal rupture was 4.09 mm, with 76.1% located in the distal ureter or ureterovesical junction. Similarly, in our study, a majority of FROU were associated with distal stones (n = 22, 68.7%). Distal stones are theorized to cause forniceal rupture due to Laplace's law (tension ∝ pressure × radius). Small stones are more likely to quickly traverse the length of the ureter. This would cause obstruction and an acute rise in pressure across the collecting system that has not had time to accommodate (i.e., dilate). The sudden increase in pressure overwhelms the tensile strength of the collecting system at the weakest point, the renal fornix.¹ Despite this, when comparing groups in our study, the location of stones was not statistically significant (p = 0.28).

Interventions and outcomes

Importantly, we found no morbidities associated to FROU, suggesting that the presence of FROU should be treated as a radiographic finding and rather raise concerns for intervention. Patients within the FROU group underwent similar rates of urologic intervention as those within the noFROU group (FROU 50% vs noFROU 48%, p = 0.86). This contrasts with other studies in which rates of urologic intervention were higher.^8,9 One more recent study by Al-mujalhem et al. retrospectively analyzed 40 patients with forniceal rupture and reported that 42.5% underwent urologic intervention. They concluded that conservative management is valid in non-complicated cases.²⁰ Within our study, the presence of FROU was not indicative of a higher likelihood of hospitalization, with similar rates of admission between the FROU and noFROU groups (37.5% vs 44.0%, respectively, p = 0.56). Thus, the presence of a forniceal rupture in the setting of an obstructing stone should not alter standard stone practice patterns. If deemed otherwise appropriate (i.e., absence of infection, intractable pain), ureteral stones with evidence of forniceal rupture are still amenable to a trial of medical expulsive therapy rather than upfront surgical intervention. Further, in the FROU group at a follow-up of 30 days, we found no evidence of complications, including re-admission, development of perinephric abscesses, urinary sepsis, or mortality. Positive urine culture was present in 31.3% patients with FROU compared with 18% of those in the noFROU cohort. Although a clinical distinction does appear to be present, this was not statistically significant, likely due to small power of analysis. Only one patient in the noFROU group returned to the emergency department after stent placement for urinary tract infection.

Limitations

There are several limitations to this study. This is a retrospective analysis with a small cohort of patients with radiographic evidence of renal forniceal rupture. The rarity of this finding is seen in our cohort, which had only 32 patients over a 3-year timeframe at an urban tertiary care center. A multi-institutional review in the future may help mitigate this limitation and provide more substantial power for an analysis. There was also no long-term follow-up for this study, however this is typical for most patients who present for obstructing ureterolithiasis.

In addition, diagnosis of forniceal rupture in this study is based largely on non-contrast cross-sectional imaging. Due to lack of contrast, it is often difficult to distinguish perinephric stranding secondary to pyelolymphatic backflow vs true perinephric fluid collections from forniceal rupture. This is reflected in our data analysis in which only degree of perinephric stranding remained statistically significant after multivariate analysis. True objective detection of forniceal rupture would require evidence of contrast extravasation into the perirenal space. Non-contrast helical CT scan of the abdomen and pelvis in the setting of acute flank pain is often the preferred initial imaging study to detect obstructing nephrolithiasis.²¹ The diagnosis of FROU will most often be inferred based on non-contrast imaging and clinical correlation. Within this analysis, prospective review by an attending radiologist and repeat review of imaging by a separate radiologist at the time of data collection were performed to confirm suspicion of FROU. We believe that this study represents the most common clinical scenario in which a urologist will encounter this diagnosis and thus provides clinically relevant data.

Another limitation is that although we find a strong presence of diabetes and hypertension in patients with FROU, we have no objective measures of a renovascular disease's relationship to intrarenal pressure. Consequently, the relationship of metabolic disease to FROU can be only associative and further physiological study would need to be performed to support this claim.

Conclusion

FROU may be an alarming reported finding but its presence does not appear to impact clinical outcomes or affect urological management, including admission or need for urologic intervention.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

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