A Case of Pure Matrix Ureteral Stone: A rare type of urinary calculi that may be overlooked

Organic Matrix Derived from Host-Microbe Interplay Contributes to Pathological Renal Biomineralization

Matrix stones are a rare form of kidney stones. They feature a high percentage of hydrogel-like organic matter, and their formation is closely associated with urinary tract infections. Herein, comprehensive materials and biochemical approaches were taken to map the organic-inorganic interface and gather insights into the host-microbe interplay in pathological renal biomineralization. Surgically extracted soft and slimy matrix stones were examined using micro-X-ray computed tomography and various microspectroscopy techniques. Higher-mineral-density laminae were positive for calcium-bound Alizarin red. Lower-mineral-density laminae revealed periodic acid-Schiff-positive organic filamentous networks of varied thickness. These organic filamentous networks, which featured a high polysaccharide content, were enriched with zinc, carbon, and sulfur elements. Neutrophil extracellular traps (NETs) along with immune response-related proteins, including calprotectin, myeloperoxidase, CD63, and CD86, also were identified in the filamentous networks. Expressions of NETs and upregulation of polysaccharide-rich mucin secretion are proposed as a part of the host immune defense to "trap" pathogens. These host-microbe derived organic matrices can facilitate heterogeneous nucleation and precipitation of inorganic particulates, resulting in macroscale aggregates known as "matrix stones". These insights into the plausible aggregation of constituents through host-microbe interplay underscore the unique "double-edged sword" effect of the host immune response to pathogens and the resulting renal biominerals.

Radiolucent Matrix Stones in a Transplanted Kidney: A Case Report

Matrix stones are a rare form of kidney stones, which are composed of mucoproteinaceous material. They are often difficult to diagnose as they are characteristically radiolucent on CT urinary tract. This difficulty is compounded in transplanted kidneys as obstructing stones commonly present without pain and can cause acute kidney injury. Here, we present a case of a 61-year-old female with a live-donor kidney transplant, who was found to develop deranged renal function on routine follow-up investigations. Therefore, a CT urogram was performed and it showed filling defects in the renal pelvis and upper ureter of the transplanted kidney. Therefore, diagnostic ureterorenoscopy was performed and three stones of about 7-8 mm each were found in the renal pelvis, they were treated by Holmium:Yttrium aluminium garnet (YAG) laser fragmentation. This case report describes the challenges in the management of this rare stone in a transplanted kidney.

Comparison of Perioperative Outcomes and Clinical Characteristics of Calcium, Matrix and Struvite Stones From a Single Institution

OBJECTIVE

To define risk factors and perioperative outcomes for matrix stones and compare these outcomes with struvite and calcium stone cohorts.

METHODS

A retrospective cohort study comparing matrix stones (n=32), struvite stones (n=23) and a matched, calcium stone control group (n=32) was performed. Two-way ANOVA was used to compare the groups for continuous variables. Chi-square tests were used to compare categorical variables. Significance was set at P <.05. All statistical tests were performed using R (v1.73).

RESULTS

We identified no differences in age, gender, or BMI between the three groups. Matrix and struvite stones were more likely to have a history of prior stone surgery and recurrent UTIs compared to calcium stones (P=.027 and P <.001, respectively). Struvite stones were more likely to present as staghorn calculi compared to matrix or calcium stones (56.5% vs 21.7% vs 18.8%, P=.006). There were no significant differences in postoperative stone free rates (P=.378). No significant differences in postoperative infectious complications were identified. Matrix stones were more likely to have Candida on stone culture compared to the struvite or calcium stones (P <.0001).

CONCLUSION

Matrix and struvite stones were more likely have a history of stone surgery and preoperative recurrent UTIs. Struvite stones were more likely to present as staghorn calculi. Matrix stones were more likely to have Candida present in stone cultures. However, no difference in postoperative infectious outcomes or stone free rates were identified. Further study with larger cohorts is necessary to distinguish matrix stone postoperative outcomes from struvite and calcium stones.