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Article

Anatomical and Histological Analyses of Rare Pancake Kidney

by
Lindsey Koper
*,
Rachell L. Quarles
,
Janine M. Ziermann-Canabarro
,
Tashanti Bridgett
,
Paola Correa-Alfonzo
and
Sulman J. Rahmat
Department of Anatomy, College of Medicine, Howard University, Washington, DC 20059, USA
*
Author to whom correspondence should be addressed.
Anatomia 2024, 3(3), 202-214; https://doi.org/10.3390/anatomia3030016
Submission received: 14 July 2024 / Revised: 30 August 2024 / Accepted: 11 September 2024 / Published: 13 September 2024
Browse Figures
Figure 1
<p>Overview of the position of the pancake kidney in relation to the posterior abdominal structures. The gastrointestinal organs in the abdominal cavity were removed. Abbreviations: a., artery; v., vein. White square = 1 cm length.</p> "> Figure 2
<p>Blood supply of the pancake kidney. (<b>A</b>) Anterior view of the kidney showing two separate renal hila circled by the dotted lines and exposed renal pelvises. (<b>B</b>) Posterior view of kidney, with the posterior arterial supply lifted by a metal probe. (<b>C</b>) Anterior view of the superior right portion of the kidney. (<b>D</b>) Left lateral view of the kidney showing the arterial supply to the left half. A metal probe is being used to lift the kidney. Abbreviations: a., artery; AA, abdominal aorta; IVC, inferior vena cava; v., vein. White square = 1 cm length.</p> "> Figure 3
<p>Example of vasculature measurement. This is a measurement from the termination of the left suprarenal vein into the inferior vena cava to the termination of all the right renal veins into the inferior vena cava. This measurement is not recorded in <a href="#anatomia-03-00016-t002" class="html-table">Table 2</a>.</p> "> Figure 4
<p>Anatomy of the pancake kidney. (<b>A</b>) Anterior view of the pancake kidney after removal from body cavity. (<b>B</b>) Diagram of estimated time frame between 6 and 9 weeks when fusion of both early-forming kidneys mostly likely occurred (modified from [<a href="#B2-anatomia-03-00016" class="html-bibr">2</a>]). (<b>C</b>) Internal view of the anterior half of the kidney. (<b>D</b>) Internal view of the posterior half of the kidney. White square = 1 cm length.</p> "> Figure 5
<p>Histology of the normal (<b>A</b>) and abnormal (<b>B</b>) kidneys, with enlarged regions indicated by the yellow boxes. Both were stained with H&amp;E. (<b>B</b>) Almost all structures in the abnormal kidney appear different from the normal kidney. The glomerular capsule appears thinner, and the glomerular capsular (urinary) space is enlarged. The renal tubules are dilated, and their walls appear thinner and do not present with the typical macula densa. The glomerulus (renal corpuscle) appears less dense structurally and abnormally formed. Finally, there is an increased amount of abnormal interstitial fluid (yellow star) between tubules. Scale bar = 100 microns.</p> "> Figure 6
<p>Histology of the adrenal gland from the pancake kidney donor (H&amp;E-stained Histoplast section). Both adrenal glands were flattened but still appeared to have both cortex (C) and medulla (outlined and labeled with M) present within the histological sectioning. Scale bar = 100 microns.</p> ">
Versions Notes

Abstract

:
During anatomical dissection of a female body donor at the Howard University College of Medicine, a rare renal anomaly was discovered. Detailed anatomical and histological analyses on this anomaly were compared to a normal kidney from another donor and previously published reports from a comprehensive literature review. Anatomical assessment confirmed the condition of pancake kidney, a rare form of completely fused, ectopic kidneys without an isthmus. Due to the lack of symptoms in patients with this condition and the limited number of published case reports, very little information is available regarding the anatomy, development, and histology of pancake kidneys, making it difficult to determine an accurate estimate of the number of individuals who are affected. In the case presented here, a single kidney was located in the pelvis, below the bifurcation of the abdominal aorta into the common iliac arteries. The histological analysis of the pancake kidney revealed focal segmental glomerulosclerosis, dilated renal tubules, and increased interstitial fluid, all common characteristics of renal disease and not present in the normal kidney of the other donor. Future studies are needed to compare the histology of pancake kidneys and typical kidneys in order to help determine potential pathologies.

1. Introduction

The urogenital system is the combination of organs and structures related to both reproduction and the formation and drainage of urine. The urinary system generally includes two kidneys, two ureters, one bladder, and one urethra. In typical human renal or kidney development, the permanent (metanephric) kidneys develop bilaterally in the sacral region of the developing embryo [1]. By gestational week 10 (8 weeks after conception), the permanent kidneys gain function and begin to ascend from the pelvis to the lower thoracic region of the embryo, ultimately meeting with the suprarenal glands in the perirenal space [1,2]. This process is complex and changes in gene expression or tissue interaction can result in a wide variety of abnormalities, collectively referred to as congenital anomalies of the kidney and urinary tract (CAKUT; [3,4,5]).
The types of CAKUT can be categorized based on position, vascularization, and abnormal rotation of the affected kidneys (Table 1; [6]). Notably, these categories can occur either independently or in concurrence. Regardless, they are still classified as different types of renal abnormalities. The most common forms of CAKUT are those resulting in renal ectopia, i.e., the abnormal location of one or both kidneys, due to an interruption in the normal embryological migration of the kidneys [7,8]. Cases of renal ectopia within the pelvic region typically have anteriorly placed renal pelvises and tend to retain primitive vascular supply, with arterial branches from the common iliac arteries and the inferior abdominal aorta [8,9,10].
There are two types of renal ectopia: (1) simple, where one kidney is abnormally placed but on the correct side of the abdomen, and (2) crossed, where one or both kidneys cross the abdominal midline (Table 1; [8]). Crossed renal ectopia can be further classified into four types, as seen in Table 1, based on how many kidneys are affected and whether there is fusion [11,12].
Renal fusion itself is one of the rarer forms of CAKUT, classified based on both the amount of visible fusion and if a kidney has crossed over the midline. The most common form of renal fusion is the horseshoe kidney, which does not involve either kidney fully crossing the abdominal midline and has an observed connection between the two fused kidneys called an isthmus [12,13,14]. The position and pathway of a kidney’s ureter is the main factor in determining whether a kidney has crossed the midline or not. For a horseshoe kidney, both ureters are present and follow the same general pathway as in non-fused kidneys.
The next most common fusion type has distinct renal crossing (i.e., crossed renal ectopia), estimated to be found in 1:7500 autopsies, and has five forms (Table 1) based on shape [13,14]. The lump and disc forms exhibit the most amount of fusion, whereas the other forms (inferior crossed, S-shaped, L-shaped, superior crossed) exhibit extreme renal crossing. The rarest form of renal fusion is the pancake kidney, estimated to occur in 1:65,000–375,000 individuals; it is visibly similar to the horseshoe kidney, but unlike the lump and disc kidney, there is no crossing over the midline [11,15,16].
The pancake kidney receives its name from its flattened shape and the complete fusion of both kidneys without the presence of an isthmus [13,17,18]. Although the kidney appears flattened, the anterior surface is commonly lobulated with multiple sources of vasculature, while the posterior surface is smooth and concave [19]. The vascularization of pancake kidneys tends to retain primitive arterial blood supply from multiple sources and venous drainage via numerous vessels [10,19,20]. The ureter placement is usually typical, with two ureters on either poles of the kidney that exit from separate renal pelvises anteriorly.
As described above, there are many known varied forms of CAKUT, but there are too few described specific cases within the current literature to ascertain how these morphologies affect a person’s lifestyle. Most of the information regarding these renal abnormalities is found accidentally in living patients during CT scans or X-rays for unrelated issues. Typically, these patients do not report any pain or other symptoms regarding their urinary tract [21]. Notably, information regarding the types of renal anomalies from previous studies has been updated in recent years, making it more difficult to correlate accurate identifications from these case study publications. Otherwise, other information comes from cadaveric dissections where very little is known about the person’s medical history and whether the observed renal morphologies are attributed to only the anomaly or influenced by pathology.
In this study, we observed a type of fused renal anomaly described as a pancake kidney in a body donor during anatomical lab dissection. We present both gross anatomical and histological descriptions of this specific anomaly. This study will expand upon the currently limited descriptions, as there are only a handful of published cases of renal abnormalities and even fewer cases that explore both histology and gross morphology. Combining histological analyses with morphological examination presents the unique ability to demonstrate potential functional deficits of renal disease in patients with this congenital anomaly, something rarely covered in the current literature.

2. Materials and Methods

2.1. Gross Anatomy

During a routine anatomical lab dissection, a fused kidney variation was identified in a 72-year-old African American female body donor (Figure 1) at Howard University College of Medicine (HUCM). A typical kidney was obtained for comparison from an 85-year-old African American male donor. Both donated their bodies to the Anatomical Donor Program in the Department of Anatomy at the Howard University College of Medicine in Washington D.C. (USA). Prior to the removal of the kidneys, all gastrointestinal tract-related systems were removed in both donors.
For the African American female donor body, the suprarenal glands were found in a normal position, but the abnormal kidney was identified in the lower abdominopelvic cavity. The abnormal kidney and suprarenal glands were photographed in situ using a Canon EOS Rebel T7 (Canon U.S.A, Inc., Melville, NY, USA) megapixel digital camera with 24–105 mm and 18–55 mm zoom lenses. Measurements of the blood vessels supplying the abnormal kidney and suprarenal glands were taken from their initial source to their termination (see Results in Section 3). The abnormal kidney and suprarenal glands were then removed by severing vasculature and any soft tissue attachment.
The kidneys of the African American male donor were also removed in order to compare the gross anatomy and histology between these kidneys and the abnormal, fused kidney.

2.2. Histological Analysis

The removed kidneys were cut coronally using a scalpel, providing an anterior and posterior section for each organ. From the abnormal kidney, two portions of about 3.375 cm3 were removed using a scalpel from the anterior half and one portion from the posterior half for histological study. The typical comparison kidney had two similar portions removed for histological analysis, one from the anterior half and the other one from the posterior half.
The suprarenal glands from both donors were collected by severing their vasculature. One abnormal and one typical suprarenal gland was used for the histological analysis. Both glands were small enough to be embedded as a whole mount. Specimens not used for histological analysis were stored in 2% paraformaldehyde (PFA).
All specimens used for histological analysis were dehydrated via an ethanol (EtOH) series with each step lasting one hour (70%, 90%, 100%, 100% EtOH). This was followed by submerging them twice in one hour in Xylene and overnight submerging in Histoplast paraffin at 62 °C overnight in a closed container. The next morning, the specimens were transferred to fresh Histoplast and left at 62 °C overnight in an open container. All specimens were subsequently embedded at room temperature into Histoplast; the forms were hardened at room temperature for two hours, mounted on a plastic holder, and then stored until sectioning in a refrigerator at 4 °C.
The embedded specimens were sectioned using a Rotary Microtome, LEICA RM2255 model, at a thickness of 7–10 μm. The thickness of the sections varied due to the rubber-like condition of the treated organs after the embedding, causing unequal thickness in the sections. About every fourth slice was collected to allow different depths of each specimen to be observed under the microscope. The sections were deparaffinized, stained with H&E (Hematoxylin and Eosin, staining kit from Abcam, Cambridge, MA, USA #ab245880), and covered with Kleermount before observation of the tissues under a microscope with an attached NIKON camera (Nikon Inc., Melville, NY, USA).

3. Results

3.1. Gross Anatomical Description

Upon dissection of the posterior abdominal wall of the female body donor, both renal cavities were empty, and a large (10 cm wide) flattened mass, later identified as the kidney, was located posterior and slightly inferior to the cecum of the large intestines in the pelvic cavity. The kidney was located slightly inferior to the bifurcation of the left and right common iliac arteries and anterior to the right common iliac artery as it deviated to the right along the pelvic inlet (Figure 1). In the abdominal cavity of this donor, dense tissue adhesions were observed along the pubic region of the posterior aspect of the anterior abdominal wall, as well as throughout the small intestines. Additionally, the donor underwent a complete hysterectomy during their lifetime, i.e., the uterus, both ovaries, and the uterine tubes were removed.
The anterior surface of the kidney was uneven, lobulated, and vascularized, while the posterior surface was smooth with arterial contributions of the median sacral artery and two accessory blood vessels referred to as posterior left and right arteries (Figure 2B). Arteries from the right and left common iliac arteries supplied the anterior and posterior sides of this kidney (see measurements in Table 2 and example of a measurement in Figure 3). Along with the anterior blood supply, two ureters were observed exiting the hila anteriorly, descending, and draining into the bladder posteriorly. The left hilum was more inferior than the right, and thus the left ureter was shorter (9.8 cm) compared to the right (10.5 cm).
A main arterial branch emerged from both the right and left common iliac arteries, and these vessels divided into anterior and posterior branches (Figure 2). The anterior branches (anterior left a. and anterior right a.) penetrated the kidney via the hila, while the posterior branches (posterior left a. and posterior right a.) penetrated the posterior surface of the kidney. As for the venous drainage (Figure 2 and Figure 4), the left and right portions of the kidney were not symmetrical in the number of vessels nor in how they connected to the inferior vena cava. The left side (Figure 2A,B) had two anterior renal veins, somewhat connected to each other, emerging from the hilum (Figure 4A) and joint together (Figure 2A) before draining into the left common iliac vein.
The more lateral anterior vein on this left side also has an additional contribution coming from the more superior border of the kidney (Figure 2A). The right side has three veins emerging from the most superior portion of the posterior side of the kidney (Figure 2C) that drain directly into the inferior vena cava. Upon further exploration, the most medial of the three veins also has a contribution that drains from the right hilum that is found deep to the entrenched renal pelvis (Figure 2A,C,D).
The bisection of the fused kidney (Figure 4C,D) revealed a mix of typical and atypical characteristics. The kidney was surrounded by a thin capsule overlaying a cortex which surrounded disorganized renal (medullary) pyramids. The renal columns are not clearly recognizable, but there are large comparable sections of cortex interdigitating. There is no visible distinction between the medulla layer of the two fused kidneys, and within this internal layer, the renal pyramids are scattered throughout and appear to fuse together, lacking the typical organized ‘pinwheel’ morphology. Many renal pyramids do not show obvious connections to the minor and major calyxes to either renal pelvis, which were not located in the typical central region of each renal pole. Some renal papillae of the pyramids closest to the left renal pelvis were visible and showed connections leading to minor calyces (Figure 4C).
Both suprarenal glands were flattened and found at their normal vertebral levels (Figure 1), surrounded by connective tissue and an anastomotic vasculature network. The left suprarenal gland had a single vein exiting its medial surface. This suprarenal vein received drainage from the left ovarian vein before draining into the inferior vena cava. A single vein was similarly seen exiting the right suprarenal gland and draining directly into the inferior vena cava.
The arterial supplies for both glands were unintentionally removed prior to their discovery and therefore cannot be described here. Initially, only the left suprarenal gland was found due to the atypical morphology of the liver, with its right lobe protruding inferiorly rather than laterally (Figure 1). The right suprarenal gland was eventually found posterior to the elongated right lobe of the liver.
Based on the previously described characteristics, we classify this renal anomaly as a pancake kidney due to the fusion of both kidneys without an isthmus and neither of the two ureters crossing the midline of the body.

3.2. Histology

The pancake kidney had several histological anomalies (Figure 5B). The glomerulus is the filtration unit and consists of a specialized bundle of capillaries, which were densely packed in the normal kidney but appeared loosely packed in the abnormal kidney. The glomerular capsule, also called Bowman’s capsule, which surrounds the glomerulus, appeared thinner in the abnormal kidney. Combined with the abnormal glomerulus, the thin glomerular capsular wall resulted in an enlarged glomerular capsular (urinary) space. In the typical kidney (Figure 5A), the glomerular capillaries appear full and fill the urinary space. Within the pancake kidney, many of the renal tubules seem dilated and their walls thinner than typical. There also appears to be an increase in interstitial fluid between the tubules. A clear macula densa, typically found in distal convoluted tubules, could not be observed when compared to the normal kidney (Figure 4A,B).
The histology of the suprarenal gland from the donor with the pancake kidney shows clear distinctions between the cortical and medullary layers (Figure 6). The cortical layer (‘C’) is lighter in color compared to the darker medullary layer (outlined with the dotted line and labeled with ‘M’), as seen in typical histology. Within the cortical layer, the three zones were very thin, mostly likely due to the organs being flattened. With increased magnification, the typical cellular characteristics were observed in the cortical layer, allowing for the identification of the three zones: zona glomerulosa, zona reticularis, and zona fasciculata. Due to difficulties with sectioning, the typical suprarenal gland could not be used.

4. Discussion

The atypical kidney exhibits characteristics consistent with observations in pancake kidney case reports. A pancake kidney is described as an irregular fusion of both kidneys located in the pelvic cavity [8,22]. In this case study, the kidneys were fused asymmetrically, forming a ‘T’ shape, with the right side more medially rotated. In addition to its irregular shape, the following characteristics are consistent with other case reports of pancake kidneys: complete fusion of the kidneys without the presence of an isthmus, anteriorly located collecting systems draining either pole of the kidney, and two separate ureters that do not cross the midline, draining into the typical location in the bladder [8,23,24]. While the number of blood vessels supplying the kidney may vary from one case to another, the blood supply from the common iliac arteries matches the primitive vasculature acquired early during development [10,19,20].
Currently, with close to 30 published case reports, the pancake kidney is estimated to be present in 1 in 65,000–375,000 individuals [15,25]. In general, the incidence of this anomaly appears to be higher in males than females, and the age at which it is discovered does not appear to be significant [24,26]. Typically, patients are unaware that they have this condition until they have abdominal screenings for complaints unrelated to the anomaly. Only a few symptoms have been directly related to the pancake kidney and other types of CAKUT, which include lower abdominal discomfort, hydronephrosis, kidney stones, recurrent urinary tract infections, or difficulty urinating [8,27,28]. There are some reported cases of congenital anomalies such as where the kidney fuses to the pelvis causing associated vertebral or rib anomalies [8,28]. The pancake kidney included in this study did not fuse to the pelvis, and the donor did not appear to have any vertebral anomalies.
Pancake kidneys result from abnormalities early during embryonic development, prior to the ascension of the kidneys [12]. The kidney passes through several developmental stages: pro-, meso-, and metanephros. The pronephros is only briefly present and never functional, while the mesonephros is shortly functional and then degenerates completely in female embryos, leaving some derivatives from the mesonephric duct in the male embryo. The metanephros will form the final kidney in the pelvis and then ascend to the upper area of the posterior abdominal wall. One hypothesis is that the embryologic vasculature that supplies the metanephric kidney acts as an anchor, drawing the bilateral metanephric kidneys closer together, ultimately resulting in renal fusion [20]. Alternatively, the kidneys could be fused in the midline with overlying vascularization preventing them from ascending, basically keeping the fused kidney in the pelvic or, sometimes, sacral regions. As a result of the failed medial rotation, the vasculature enters the hila, forming a “vasculature barrier”, which prevents the migration of the kidney [8,15,29]. Our case study demonstrates an example of fused kidneys that failed to completely rotate medially, providing anteriorly placed pelvises [12,23]. The embryological vasculature enters the renal hila normally, but it is common for accessory arteries not to enter the renal hila [12,29], as observed in this case study, with several arteries entering the posterior surface of the pancake kidney.
The urinary and reproductive systems are developmentally and functionally linked with each other and are therefore called the urogenital system. The urinary system and reproductive system both derive from the urogenital ridge. With the close interaction during the development of these two systems, any abnormalities that occur in one system can potentially impact the other [20,30]. Other noted complications of renal anomalies include observations of duplications of ureters, undescended testes, and abnormal development of the uterus [28]. Based on the observed anatomy of the donor with the abnormal kidney combined with the complete hysterectomy, one could speculate that the donor had an abnormally developed female reproductive tract. However, we have no information regarding the medical history of the donor and why the hysterectomy was performed. Also, hysterectomies can be performed for a multitude of issues. The vaginal canal did not show any apparent abnormalities.
Other anatomical abnormalities that develop as a result of ectopic kidneys can be observed with respect to the suprarenal gland. In the donor with the abnormal kidney, both the right and left suprarenal glands were completely flattened, termed a “lying-down” suprarenal gland [30,31]. This anatomical variation is observed in patients with an empty renal fossa due to renal agenesis or renal ectopia, suggesting that the kidneys are responsible for forming the typical triangular shape of the suprarenal glands [31]. Although anatomical malformations of the suprarenal glands were observed in this report, the vertebral level locations of both glands and the histological analyses were normal, despite the flattened shape.
The histology of the pancake kidney showed three main characteristics which were not observed in the normal kidney: (1) dilated tubules; (2) the increased presence of interstitial fluid; and (3) “shrunken” glomeruli. The presence of dilated tubules and increased interstitial fluid observed in the abnormal kidney are common indicators of chronic kidney disease [32]. Chronic kidney disease is a slow, progressive disease where the kidneys lose their function to filter blood [33]. Due to its gradual worsening, chronic kidney disease often goes undetected in affected patients [34]. While the specific cause of this disease varies, there appears to be a correlation between the development of renal disease and patients with dementia and cachexia [35,36,37,38,39], which is the reported cause of death for the donor with the pancake kidney.
The “shrunken” glomeruli are referred to as collapsed glomerular tufts, signs of focal segmental glomerulosclerosis (FSGS; [40]). FSGS is a disease that leads to scarring of portions of the glomerular capillaries [41,42]. The most common outcome for patients with FSGS is the manifestation of nephrotic syndrome [42], which is a renal disorder that increases the passing of protein in urine due to glomerular scarring [43,44]. Common side effects of nephrotic syndrome are fatigue and appetite loss [42,44], similar to the main symptoms of cachexia, which the donor with the pancake kidney in our study suffered from.
Even though the medical records of the donor with the pancake kidney do not specify any renal complications, histological findings from this study suggest the presence of renal disease. This is further supported by the donors’ cause of death, increasing the likelihood of the presence of chronic kidney disease. Based on the histological examination of the normal kidney from another donor present at the same time in the same anatomical donor program and embalmed by the same diener, the abnormal findings were not caused by the embalming/preservation process, further supporting the likely presence of renal disease.
Glenn [23] presented a case report of a horseshoe kidney and suggested that the fusion of kidneys would cause the development of renal cysts, dilated tubules, and “immature glomeruli”, similar to what was seen in the pancake kidney within this study. Today, it is understood that anatomical abnormalities, such as the pancake kidney, rarely contribute to the development of renal disease characteristics in adults [45]. Likely, asymptomatic adult patients develop renal disease characteristics from other underlying factors such as high blood pressure or diabetes, and not from the fused kidney itself [33,34,35,36,37,38,39,40,41,42,43,44,45]. Although several pancake kidney case reports have been published since 1958, there is virtually nothing known about the histology of those cases. With little information on the histology of pancake kidneys, it is difficult to determine if the observed cellular characteristics are typically found in patients with this anomaly without the collection of more data.

5. Conclusions

Abnormalities of the urinary system can present in many different forms. One of the rarest types of congenital renal abnormalities is the pancake kidney, making it difficult to estimate the number of individuals who are affected. Due to the limited number of case reports, very little information is available regarding the anatomy and histology of this anomaly.
This study describes a pancake kidney in a female body donor. Although it is not fully understood how this anomaly developed, the fusion of both kidneys occurred early on in development, and the retention of the primitive vascular supply contributed to the establishment of the fused kidney in the pelvis. The only associated anatomical abnormalities observed were of the flattened suprarenal glands, a consistently observed anomaly in cases of ectopic kidneys.
The histological analysis of the pancake kidney in this study confirms abnormal cellular arrangements, which are commonly associated with renal disease. The donor’s cause of death is also strongly correlated with the occurrence of renal disease, suggesting that most likely the donor developed renal disease due to underlying factors. The relative lack of studies of pancake kidney histology and potential external contributing factors make it difficult to definitively conclude if and when the donor developed renal disease. Further studies are needed to compare the histology of pancake kidneys and typical kidneys to aid in determining potential characteristic pathologies.

Author Contributions

All authors contributed to the conceptualization of this project. S.J.R. and L.K. supervised this project. Gross anatomical dissection, measurements, descriptions, and associated figure plates, plus literature search, were carried out by L.K., R.L.Q. and T.B. Histology was performed by R.L.Q., P.C.-A. and J.M.Z.-C. Histology figures plates were created by J.M.Z.-C. L.K. wrote the manuscript, and R.L.Q., J.M.Z.-C. and S.J.R. reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki The Office of Regulatory Research Compliance determined the study to be exempt based on 45 CFR 46.101(b)(4) and involves minimal risk (Howard University IRB Federal Wide Assurance number FWA00000891).

Informed Consent Statement

Not applicable.

Data Availability Statement

All relevant original data are presented in this manuscript and therefore are included in the article; further inquiries can be directed to the corresponding author.

Acknowledgments

We want to thank the reviewers and editors for their suggestions and critiques, further strengthening this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Overview of the position of the pancake kidney in relation to the posterior abdominal structures. The gastrointestinal organs in the abdominal cavity were removed. Abbreviations: a., artery; v., vein. White square = 1 cm length.
Figure 1. Overview of the position of the pancake kidney in relation to the posterior abdominal structures. The gastrointestinal organs in the abdominal cavity were removed. Abbreviations: a., artery; v., vein. White square = 1 cm length.
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Figure 2. Blood supply of the pancake kidney. (A) Anterior view of the kidney showing two separate renal hila circled by the dotted lines and exposed renal pelvises. (B) Posterior view of kidney, with the posterior arterial supply lifted by a metal probe. (C) Anterior view of the superior right portion of the kidney. (D) Left lateral view of the kidney showing the arterial supply to the left half. A metal probe is being used to lift the kidney. Abbreviations: a., artery; AA, abdominal aorta; IVC, inferior vena cava; v., vein. White square = 1 cm length.
Figure 2. Blood supply of the pancake kidney. (A) Anterior view of the kidney showing two separate renal hila circled by the dotted lines and exposed renal pelvises. (B) Posterior view of kidney, with the posterior arterial supply lifted by a metal probe. (C) Anterior view of the superior right portion of the kidney. (D) Left lateral view of the kidney showing the arterial supply to the left half. A metal probe is being used to lift the kidney. Abbreviations: a., artery; AA, abdominal aorta; IVC, inferior vena cava; v., vein. White square = 1 cm length.
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Figure 3. Example of vasculature measurement. This is a measurement from the termination of the left suprarenal vein into the inferior vena cava to the termination of all the right renal veins into the inferior vena cava. This measurement is not recorded in Table 2.
Figure 3. Example of vasculature measurement. This is a measurement from the termination of the left suprarenal vein into the inferior vena cava to the termination of all the right renal veins into the inferior vena cava. This measurement is not recorded in Table 2.
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Figure 4. Anatomy of the pancake kidney. (A) Anterior view of the pancake kidney after removal from body cavity. (B) Diagram of estimated time frame between 6 and 9 weeks when fusion of both early-forming kidneys mostly likely occurred (modified from [2]). (C) Internal view of the anterior half of the kidney. (D) Internal view of the posterior half of the kidney. White square = 1 cm length.
Figure 4. Anatomy of the pancake kidney. (A) Anterior view of the pancake kidney after removal from body cavity. (B) Diagram of estimated time frame between 6 and 9 weeks when fusion of both early-forming kidneys mostly likely occurred (modified from [2]). (C) Internal view of the anterior half of the kidney. (D) Internal view of the posterior half of the kidney. White square = 1 cm length.
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Figure 5. Histology of the normal (A) and abnormal (B) kidneys, with enlarged regions indicated by the yellow boxes. Both were stained with H&E. (B) Almost all structures in the abnormal kidney appear different from the normal kidney. The glomerular capsule appears thinner, and the glomerular capsular (urinary) space is enlarged. The renal tubules are dilated, and their walls appear thinner and do not present with the typical macula densa. The glomerulus (renal corpuscle) appears less dense structurally and abnormally formed. Finally, there is an increased amount of abnormal interstitial fluid (yellow star) between tubules. Scale bar = 100 microns.
Figure 5. Histology of the normal (A) and abnormal (B) kidneys, with enlarged regions indicated by the yellow boxes. Both were stained with H&E. (B) Almost all structures in the abnormal kidney appear different from the normal kidney. The glomerular capsule appears thinner, and the glomerular capsular (urinary) space is enlarged. The renal tubules are dilated, and their walls appear thinner and do not present with the typical macula densa. The glomerulus (renal corpuscle) appears less dense structurally and abnormally formed. Finally, there is an increased amount of abnormal interstitial fluid (yellow star) between tubules. Scale bar = 100 microns.
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Figure 6. Histology of the adrenal gland from the pancake kidney donor (H&E-stained Histoplast section). Both adrenal glands were flattened but still appeared to have both cortex (C) and medulla (outlined and labeled with M) present within the histological sectioning. Scale bar = 100 microns.
Figure 6. Histology of the adrenal gland from the pancake kidney donor (H&E-stained Histoplast section). Both adrenal glands were flattened but still appeared to have both cortex (C) and medulla (outlined and labeled with M) present within the histological sectioning. Scale bar = 100 microns.
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Table 1. Classification of upper urinary tract anomalies (modified from [8]).
Table 1. Classification of upper urinary tract anomalies (modified from [8]).
Categories of Renal AnomalyKey Characteristics
Renal Position
Simple Renal EctopiaAt least one kidney not in normal position but neither kidney has crossed the midline
Crossed Renal EctopiaAt least one kidney not in normal position which has crossed the midline with its ureter inserted normally
BilateralBoth kidneys have crossed the midline
Solitary KidneyPresence of single kidney that has crossed the midline
Without FusionCrossed kidney does not fuse to typically placed one
With FusionCrossed kidney fuses to non-crossed kidney
Inferior CrossedSuperior pole of crossed kidney fuses to inferior pole of normal kidney
S-shapedCrossed kidney is located inferiorly with renal pelvis oriented laterally
LumpBoth kidneys are fused but one of the kidneys has crossed midline
L-shapedCrossed kidney is orientated perpendicular to the inferior pole of the normal kidney
DiscBoth kidneys are fused along the medial portions with one kidney crossing midline
Superior CrossedInferior pole of crossed kidney fuses to superior pole of normal kidney
Renal Form (Fusion)
HorseshoeTypically, only inferior poles fuse but sometimes both superior and inferior do; presence of a fibrous isthmus between both kidneys
PancakeComplete fusion of both kidneys due to lack of renal capsule with no isthmus
Table 2. Measurements of arteries related to the pancake kidney in this study.
Table 2. Measurements of arteries related to the pancake kidney in this study.
Blood SupplyLength (cm)
Left common iliac artery to left renal pelvis6.4
Left common iliac artery to division2.4
Anterior left arterial branch from division4.1
Right common iliac artery to right renal pelvis7.7
Right common iliac artery to division1.7
Anterior right arterial branch from division6.0
Posterior right arterial branch from division1.2
Median sacral artery4.5
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Koper, L.; Quarles, R.L.; Ziermann-Canabarro, J.M.; Bridgett, T.; Correa-Alfonzo, P.; Rahmat, S.J. Anatomical and Histological Analyses of Rare Pancake Kidney. Anatomia 2024, 3, 202-214. https://doi.org/10.3390/anatomia3030016

AMA Style

Koper L, Quarles RL, Ziermann-Canabarro JM, Bridgett T, Correa-Alfonzo P, Rahmat SJ. Anatomical and Histological Analyses of Rare Pancake Kidney. Anatomia. 2024; 3(3):202-214. https://doi.org/10.3390/anatomia3030016

Chicago/Turabian Style

Koper, Lindsey, Rachell L. Quarles, Janine M. Ziermann-Canabarro, Tashanti Bridgett, Paola Correa-Alfonzo, and Sulman J. Rahmat. 2024. "Anatomical and Histological Analyses of Rare Pancake Kidney" Anatomia 3, no. 3: 202-214. https://doi.org/10.3390/anatomia3030016

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