A Literature Review of Phantom Bladder Perforation: The Curious Case of Bladder Lipoma

Abstract

Introduction: Although lipomas are common benign tumors found in adults, lipomas of the bladder are extremely rare. Bladder lipomas are infrequently reported in the urologic literature, with only 19 cases published worldwide. These can present as a mass on cystoscopy and cause irritative voiding symptoms, depending on their location. Upon transurethral resection, seeing fat can be concerning for a perforation, as lipoma can be mistaken for extravesical fat. Hence, familiarity with this rare entity is of paramount importance for urologists to prevent unnecessary investigations and interventions that are needed in case of a true bladder perforation. Case presentation: This study presents a case of bladder lipoma in a 73-year-old male with end-stage renal disease who presented for pretransplant urologic evaluation due to microscopic hematuria and irritative lower urinary tract symptoms (LUTS). During cystoscopy, a bladder mass was seen, and a transurethral resection of the bladder tumor (TURBT) revealed bright yellow adipose tissue immediately underneath the bladder mucosa. Concerns about perforation were obviated when seeing intact detrusor muscle underneath, visually confirming the integrity of the bladder wall. The resection was completed, and the CT scan was re-read with the radiologist, which confirmed the presence of a lipoma that was missed pre-operatively due to patient’s oliguria and collapsed bladder. No catheter drainage or cystogram was performed based on these findings. Outcome: The patient healed without any complications. Histopathology confirmed the diagnosis of a mature lipoma. The patient was cleared for transplant from a urologic standpoint and had a successful renal transplantation without delay. Discussion: This case documents the anomalous occurrence of a lipoma within the bladder and supports maintaining a broad differential, including liposarcoma, angiomyolipoma, and other non-malignant fatty tumors during the evaluation of a bladder mass.

1. Introduction

Urinary bladder masses are more likely to be malignant than non-malignant, and the most common malignancy of the bladder is urothelial carcinoma. Among the 1–5% of non-malignant bladder tumors, leiomyoma is the most common histologic type [1]. Therefore, the discovery of a bladder lipoma is exceedingly rare and the literature is sparse, with only a handful of cases having been reported [2] worldwide.

Lipomas are benign, adipose containing tumors that are found in subcutaneous tissue and are the most common soft tissue tumors [3]. These tumors are most commonly found on the proximal limbs or trunk, but can also present on internal organs [4]. Lipomas typically are asymptomatic and diagnosed in patients between the ages of 40 and 60 years [5]. The malignant counterpart of a benign lipoma is liposarcoma. When malignancy is suspected, distinguishing between a lipoma and a potential liposarcoma is crucial due to their overlapping early presentations [6].

Bladder lipomas may present as encapsulated, endophytic projections from the bladder wall¹. The clinical presentation varies but is often associated with gross hematuria [7]. On imaging, these typically present as homogenous lesions with smooth margins containing macroscopic fat [2]. Prompt detection of bladder lipomas is aided by imaging and familiarity with the entity and typical characteristics.

We present a rare case of a bladder lipoma, missed on preoperative imaging and discovered intraoperatively on resection of a bladder mass, falsely raising concerns for bladder perforation.

2. Case Report

A 73-year-old male with ESRD on dialysis since 2023 presented to the clinic for pre-transplant urologic clearance due to microscopic hematuria and history of BPH with LUTS. Other pertinent past medical history included class II obesity, aortic stenosis, coronary artery disease, chronic heart failure, kidney stones, and degenerative disc disease. The patient had a remote smoking history of 2 pack-years. The patient was oliguric and had a history of LUTS with urinary urgency and nocturia. Recent urinalysis performed as part of his pre-transplant workup revealed microscopic hematuria. The prostate was noted to be enlarged and estimated to be approximately 60 g. Office cystoscopy revealed a normal urethra and a high-riding prostate. A 2 cm submucosal smooth, nodular mass was noted on the left lateral wall of the bladder, which prompted the need for CT scan, retrograde pyelograms, and TURBT of the mass. (Figure 1a).

Prior to starting TURBT, bladder washing was sent for cytology/FISH and retrograde pyelograms were found to be normal. Pan cystoscopy revealed a nodular submucosal bladder mass on the left posterior wall approaching the dome of the bladder (Figure 1b). The lesion was resected using a 25 Fr resectoscope and revealed golden yellow fatty tissue (Figure 1c) lying immediately underneath the mucosa. The startling finding of seeing fatty tissue prompted concerns for extra-vesical fatty tissue and evaluation for bladder perforation. The fat was found to be shiny, granular, and well-organized between the mucosal lining and the detrusor muscle. There was no evidence of diverticulum upon inspection of the bladder wall on cystoscopy. This fatty tissue was carefully removed by snaring with a cold loop so as to not extend the perforation if there was one.

Upon removal of the adipose tissue, we were clearly able to visualize intact detrusor muscle behind the lipoma, thus confirming that there was no bladder perforation.

Intraoperative consultation with a radiologist was obtained. On re-reading of the CT, intramural lipoma of bladder wall was confirmed. On closer examination, the read was revised, confirming that there were two hypodense lesions potentially connected by a stalk suggestive of a lipoma (Figure 2). Based on this, a decision was made not to perform an intraoperative cystogram for extravasation or to leave a catheter for drainage. The complete resection of the mass was visually confirmed. Hemostasis was achieved to satisfaction. The patient was discharged in stable condition and the mass was sent for histological evaluation.

The pathology report described the specimen as a tan-pink rubbery soft tissue mass. Microscopic analysis revealed mature adipocytes surrounded by normal bladder mucosal tissue (Figure 3). There was no concern for liposarcoma due to the absence of hyperchromasia and multinucleated stromal cells, as well as no immature/atypical lipoblasts. Both gross examination and microscopic findings supported the diagnosis of a mature lipoma. Of note, his urine cytology was negative for high-grade urothelial carcinoma.

At his follow-up appointment, the diagnosis of a bladder lipoma was discussed with the patient, and he was cleared for transplantation from a urologic standpoint. He subsequently underwent a successful renal transplantation with no urologic complications.

3. Discussion

Bladder lipomas are extremely rare, and the literature is currently limited mainly to case reports. A literature review of PubMed and EMBASE yielded only 19 English-language cases from 2001–2023 (

Table 1. Review of bladder lipomas reported in the current literature.

Author	Age	Sex	Smoking Status	Imaging	Description	Hematuria	LUTS	Management	Outcome
Eggener SE et al., 2001 [11]	53	M	30 pack-year history	CT	One, posterior wall, 13 mm	Microscopic	Not reported	TURBT	No microscopic hematuria at 1-month follow-up
Ulker S et al., 2001 [12]	32	M	Not reported	CT	One, L lateral wall, 7 mm	Microscopic	Not reported	Not reported	Not reported
Meraj S et al., 2002 [10]	53	M	20 pack-year history	Urography	One, posterior wall, not reported	Microscopic	Frequency/urgency	Cold cup biopsy	Not reported
Kunkle DA et al., 2005 [13]	48	M	Not reported	MRI	Two, anterior + L lateral wall, not reported	Not reported	Frequency/urgency	TURBT	Improved voiding symptoms at follow-up
Lang EK et al., 2005 [14]	73	M	Not reported	CT	Multiple, trigone, 6–8 mm	Gross	None	Not reported	Not reported
Lang, EK et al., 2005 [14]	54	M	Not reported	CT	Multiple, trigone, 7–9 mm	Gross	Not reported	Not reported	Not reported
Brown C et al., 2008 [15]	44	M	Not reported	MRI, USS	One, dome, not reported	Not reported	Dysuria	TURBT	Not reported
Ukita S et al., 2009 [16]	61	F	Not reported	MRI	One, R retropelvic cavity, 150 mm	Not reported	None	Total tumorectomy	Uneventful postoperative recovery
Tsui JF et al., 2013 [17]	61	F	Not reported	CT	Two, anterior wall, 12 mm & 8 mm	Microscopic	Frequency/urgency	Partial cystectomy	Marked symptomatic improvement at one-year follow-up
Akan S et al., 2014 [9]	59	F	Not reported	USS	One, R lateral, 15 mm	Microscopic	Incontinence	TURBT	Improvement in LUTS at 3-month follow-up
Ates M et al., 2015 [18]	67	F	Non-smoker	MRI, USS	One, dome, 7 mm	Normal	Dysuria	TURBT	Resolution of symptoms at 6-month follow-up
Val-Berna, JF et al., 2015 [2]	75	M	Not reported	CT	One, dome, 5 mm	Not reported	Not reported	TURBT	Uneventful recovery
Gilbert, B et al., 2018 [19]	66	M	Significant smoking history	USS	One, posterior wall, 6 mm	Microscopic	None	Cold cup biopsy	No persistent urologic symptoms at one-year follow-up
Degheili et al., 2019 [7]	61	M	Non-smoker	USS	One, right lateral wall of bladder, 1 × 1 cm,	Microscopic	None	TURBT	Follow-up lab revealed no hematuria
Ekren et al., 2019 [20]	61	M	Not reported	USS	One, posterior base of bladder, 4.9 mm	Present	Not reported	TURBT	Follow-up revealed no occurrence
Jendouzi et al., 2020 [21]	69	M	Non-smoker	No CT/USS	One, posterior wall of bladder, 5 mm,	Gross	Urinary frequency and nocturia	TURBT	Resolution of symptoms at 6-month follow-up
Panigua et al., 2020 [22]	63	M	Former smoker	USS, CT	One, right upper bladder wall, 1.8 × 1.3 × 0.9 cm,	No	PMD	TURBT	Follow-up ultrasound 3 months post-op revealed no bladder masses
Emekli et al., 2022 [23]	43	M	Not reported	CT	One, anterior bladder wall, 14 × 9 × 8 mm,	No	None	Not reported	Not reported
Kaltsas et al., 2023 [24]	68	M	Not reported	CT	One, posterior bladder wall	Gross	Not reported	TURBT	Follow-up cystoscopies and ultrasound revealed no reoccurrence

). Search terms included: “lipoma” and “bladder,” “urinary bladder” and “lipoma,” “bladder lipoma” and “benign bladder tumor,” “bladder lipoma” and “adipose tissue.” Despite lipomas being a common benign tumor found in adults, the presence of visceral lipomas, including lipomas of the bladder, are not commonly encountered in practice [2]. It is important to note that our patient did not have lipomas anywhere else on his body. Multiple lipomas throughout the body may point to rare conditions, such as familial multiple lipomatosis or Dercum’s disease [8]. Additionally, our concerns for perforation were diminished once we visualized intact detrusor muscle during TURBT. When a urologist encounters yellow adipose tissue on TURBT, several steps can be taken to rule out perforation, including observing the loss of distention, visualizing intact detrusor muscle, and performing post-op CT cystogram (Figure 4). Our report demonstrates a rare finding, as urinary bladder masses are more often found to be malignant [9]. Conversely, bladder lipomas have no risk for malignant potential [10].

3.1. Clinical Presentation

The most common presentation for a bladder lipoma is asymptomatic gross or microscopic hematuria. It is hypothesized that the hematuria may be due to excoriation of the overlying bladder lipoma mucosa [2]. Our patient presented with evidence of microscopic hematuria on recent urinalysis and lower urinary tract symptoms (LUTS). In our review of the literature, 12 of the 19 cases (63%) reported hematuria, with 7 of the 19 (37%) reporting microscopic hematuria, and 4 of the 19 (21%) reporting gross hematuria. One case did not specify gross versus microscopic hematuria. A total of 8 of the 19 cases (42%) reported LUTS. LUTS associated with bladder lipomas included urgency, frequency, dysuria, and incontinence [19]. Voiding symptoms may be secondary to local irritation of the bladder wall by the lipoma [13]. Our patient presented with both urgency and nocturia and although these symptoms may be worsened by the bladder lipoma, they are also likely due to BPH. For this reason, we do not expect complete resolution of symptoms post-TURBT, as seen in other patients with bladder lipomas [7,19,21]. Additionally, our patient underwent back surgery and had resultant spinal stenosis that coincided with the onset of urinary urgency. Therefore, it is not surprising our patient continued to endorse urgency after TURBT. One report describes a patient with a bladder lipoma and BPH, but it is unknown if urinary symptoms, including frequency and hesitancy, improved after resection, as they were not discussed [10]. Of note, only four patients in our review of the literature had a significant smoking history.

On cystoscopy, several case reports describe the lipoma as smooth, yellow, and benign-appearing [16]. This finding aligns with our lesion, which was noted as fatty/adipose-like golden tissue intraoperatively. The average size of bladder lipomas reported in the literature is around 8–9 mm when excluding a 150 mm retroperitoneal lipoma derived from the urinary bladder. The posterior bladder wall was the most commonly reported site for bladder lipomas (6 of 19 cases, 32%), though their location varies significantly in the literature. Most bladder lipomas were resected through TURBT. However, one case of an exophytic lesion was excised laparoscopically and another reported by Tsui et al. required partial cystectomy for complete resection. After resection, all case reports demonstrated improvement or resolution of symptoms associated with the lipoma. There are no reports of recurrences to date.

3.2. Differential Diagnosis

Lipomas develop from mature adipose tissue, and the appearance of the tissue on TURBT strongly suggests lipoma as the differential diagnosis for this lesion. Also on our initial differential was a urachal remnant or urachal fibrolipoma. The urachus is an embryologic structure that communicates between the urogenital sinus and umbilicus, which is usually seen in the midline close to the dome. The urachus usually regresses by birth, but remnants can persist and require surgical intervention [25]. Rarely, a calcified fibrolipoma can form within the urachus [26]. Following radiology consultation and CT findings showing no connection between the bladder and umbilicus, a urachal remnant was deemed less likely. The mass was also observed to the left of midline, away from the bladder dome.

Another important differential is liposarcoma, which requires microscopic analysis by pathology, as both lipoma and well-differentiated liposarcoma can appear similarly on gross examination. Our pathology report demonstrated mature adipocytes, which aligns with the microscopic appearance of a lipoma. Liposarcoma would demonstrate nuclear atypia and multi-nucleated stromal cells on microscopic examination [25,27].

Also on the differential, one should consider pelvic lipomatosis, which is a condition characterized by multiple lipomatous lesions arising from peri-rectal and peri-visceral fat [26,28]. Our patient was severely obese and thus had large amounts of subcutaneous and peri-vesical fat. However, this diagnosis was less likely given the presence of a solitary endophytic intramural lesion and the absence of compression of pelvic structures with excess fatty tissue.

3.3. Radiologic Findings

Suspicion for a bladder lipoma can be demonstrated on CT by the presence of a well-defined, homogenous, low-density mass [29]. Ultrasound scan (USS) and MRI are other techniques that can be used for detection of a bladder lipoma, but definitive diagnosis requires histopathological examination.

Table 2. Key features of bladder lipomas, including case-based findings in the radiologic literature.

Imaging Used	Key Features	Case-Based Imaging Findings
CT	Homogenous, endophytic, hypodense lesion with smooth margins as viewed in the non-enhanced, venous, or excretory phase (Figure 2). Fat attenuation of the lesion ≤ −20 HU, which is diagnostic of lipoma (usually −50 to −150 HU).	-Erich K. Lang et al. reported that in an excretory phase CT generating 5 mm thick slices demonstrated 7 to 9 mm grape-like lesions, with attenuation coefficient ranging from −60 to –160 HU found in the trigone region [14]. -The presence of septations as reported by Paniagua et al. (Figure 5) raised suspicion of malignant liposarcoma, which would require surgical intervention [22].
MRI	Common Features: Homogenous, endophytic bladder nodule with smooth margins.	-Chung A.D et al. reported that the visibility of lipoma can be diminished by the hyperintense signal of the nearby urine. Noting the chemical shift artifact in the frequency encode direction may help in the diagnosis [16]. -Brown C et al. reported lipoma associated with UT, a relatively rarer presentation for lipoma; the patient had a cystoscopy followed by a pelvic MRI, which revealed the lesion [15]. -An interesting case reported by Ukita S et al. revealed a lipoma in the R retropelvic cavity arising from the bladder, measuring about 15 cm as seen on T1- and T2-weighted MRI. The positions of the broad ligament, uterine ligament, and iliac arteries helped determine the location of the lesion prior to surgical intervention [16].
	T1-Weighted Sequences: Hyperintense signal due to fat content (Figure 6a) [18].
	T2-Weighted Fast Spin Echo (FSE) Sequences: Hyperintense signal due to J coupling effect (Figure 6b) [18].
	Fat-Suppressed Imaging: Hypointense signal using techniques like chemical fat suppression, inversion recovery, and Dixon methods (Figure 6c,d) [18].
US	Fatty composition showcasing homogenous, hyperechogenic lesion with endophytic growth.(Figure 7)	-Echogenicity could be very similar to the fat around the bladder, as observed by Paniagua et al., potentially mimicking an extravesical lesion pushing into the bladder (Figure 5) [22]. -In Ukita S et al.’s case of a retropelvic lipoma, TVUS revealed an echogenic mass in the right adnexal region, suggesting a mature ovarian cystic teratoma congaing fat. MRI and surgery were required for confirmation and treatment [16].

summarizes the radiological findings through common imaging modalities, we have included some unique examples for a better understanding. CT was the most common imaging technique (8 of 19 cases, 42%) utilized to identify bladder lipomas in our review of the literature. Other case reports have demonstrated discovery of the lipoma through MRI or USS, although the utility of ultrasound is limited by operator dependence and has reduced sensitivity for small lesions. Furthermore, there are cases of lipomas identified solely through cystoscopy [2,13,22,24]. Our patient underwent a CT scan as part of his pre-transplant workup and the initial read did not detect the bladder lipoma, as small lipomas can often be missed on imaging, especially with a collapsed bladder wall. However, corroborating the intraoperative findings with reexamination of his CT scan revealed two hypodense lesions. CT suggested these two lesions were likely one, connected by a thin stalk, which we also confirmed intraoperatively while removing the mass. These lesions had fat attenuation ≤ −20 HU, which indicates fat. There are several other lesions that can mimic the presence of a bladder lipoma on radiologic imaging, which include leiomyoma, hemangioma, plasmacytoma, fibroma, and neurofibroma. The ability to distinguish these entities radiologically is critical for guiding clinical management and surgical planning (

Table 3. Bladder lipoma differential diagnosis: imaging characteristics.

	Subtype	US	CT	MRI
Benign Mesenchymal Tumors		Usually, an endophytic solid smooth nodule with varying echogenicity depending on the tumor type is seen.
	Leiomyoma (most common)	Homogenous, hyperechoic, thin echogenic surface [30].	Pedunculated, homogenous, soft tissue density mass, not distinguishable from other submucosal tumors [30,31].	Homogenous, well-circumcised mass with hypointense signal on T1WI, T2WI, and DW MRI sequences. Variable contrast enhancement [32]. Presence of collagen and smooth muscle on MRI is diagnostic.
	Paragangliomas	Hypoechoic mass, doppler may reveal increased vascularity. (EUS have also been performed in a few cases) [33,34].	Well-defined, heterogenous [33], enhancing mass, similar to other mesenchymal neoplasms.	T1WI shows mild hyperintensity, T2WI reveals intermediate to high-signal-intensity “lightbulb sign” [35]. Marked diffusion restriction, strong enhancement owing to high vascularity.
	Hemangioma	Hyperechoic or mixed echogenicity with a turbulent flow on doppler	Solid to cystic lesion, small-ring calcifications representing phleboliths can be seen.	Intermediate signal on T1WI, heterogenous signal with predominant hyperintensity on T2WI.
Malignant Mesenchymal Tumors: Liposarcoma	Well-differentiated dedifferentiated, myxoid pleomorphic	Liposarcomas exhibit heterogenous, irregular-shaped appearance with variable echogenicity [36].	Solid, heterogenous, mass with irregular borders, low-grade tumors initially can present as an endophytic nodule [37]. Lesion exabits partial fat with density ranging from −50 HU to −150 HU.	Contrast-enhanced MRI reveals scattered low and high intensity areas, as seen on T2WI.
Pelvic Lipomatosis [38]		Hyperechoic fatty presentation around the bladder.	Bladder described as “pear shape ”on CECT; sigmoid compression may be seen. Unlike lipomas, lipomatosis lacks capsule and might show an irregular spread.	Homogenous overgrowth of adipose tissue surrounding the pelvic viscera, Hyperintense on T1WI and T2WI, signal annulation on fat suppression.

).

Figure 5. Reproduced with permission from Dr. Miguel Paniagua, “Urinary Bladder Lipoma: An Illustrative Case”; published by the Journal of Radiology Case Reports, 2020 [22]. Yellow arrow denotes septation in the lesion. Full uncropped images provided in Supplementary Figure S4.

Figure 5. Reproduced with permission from Dr. Miguel Paniagua, “Urinary Bladder Lipoma: An Illustrative Case”; published by the Journal of Radiology Case Reports, 2020 [22]. Yellow arrow denotes septation in the lesion. Full uncropped images provided in Supplementary Figure S4.

Figure 6. Reproduced with permission from Dr. Yigit Akin, “An extremely rare mass of bladder: lipoma in the bladder”; published by the Irish Journal of Medical Science, 2015 [18]. Pelvic magnetic resonance images. (a) Axial T1-weighted image without fat-saturation, arrow shows the lesion; (b) axial T2- weighted image without fat-saturation, arrow shows the lesion, (c) coronal post-contrast fat-suppressed T1-weighted image, arrow shows the lesion; (d) sagittal fat-suppressed T2-weighted image, arrow shows the lesion. B bladder. Full uncropped images provided in Supplementary Figure S5.

Figure 6. Reproduced with permission from Dr. Yigit Akin, “An extremely rare mass of bladder: lipoma in the bladder”; published by the Irish Journal of Medical Science, 2015 [18]. Pelvic magnetic resonance images. (a) Axial T1-weighted image without fat-saturation, arrow shows the lesion; (b) axial T2- weighted image without fat-saturation, arrow shows the lesion, (c) coronal post-contrast fat-suppressed T1-weighted image, arrow shows the lesion; (d) sagittal fat-suppressed T2-weighted image, arrow shows the lesion. B bladder. Full uncropped images provided in Supplementary Figure S5.

Figure 7. Reproduced with permission from Dr. Miguel Paniagua, “Urinary Bladder Lipoma: An Illustrative Case”; published by the Journal of Radiology Case Reports, 2020 [22]. Blue arrow denotes hyperechoic endophytic lesion which represents lipoma. Full uncropped images provided in Supplementary Figure S6.

Figure 7. Reproduced with permission from Dr. Miguel Paniagua, “Urinary Bladder Lipoma: An Illustrative Case”; published by the Journal of Radiology Case Reports, 2020 [22]. Blue arrow denotes hyperechoic endophytic lesion which represents lipoma. Full uncropped images provided in Supplementary Figure S6.

These include relatively rarer types of benign masses that arise from the submucosal layer of the bladder. Malignant lesions to consider while imaging include liposarcomas.

Teaching point: Under normal imaging conditions, the contours and margins of the urinary bladder are smooth, and optimal fluid distention is required for evaluation. Retrograde saline filling of the urinary bladder and adequate distention improves the ability to detect small lesions that may be difficult to evaluate in oliguric and non-distended urinary bladder. Normal bladder wall thickness: ≤3 mm, uniform when distended and ≤5 mm when collapsed. Standard imaging in oliguric patients is focused on finding obstructing pathologies; in such cases, benign lesions like lipomas may be overlooked. Suboptimal bladder distention can pose as artifactual thickening, which, in most cases, pathological evaluation of the bladder mass is necessary to determine the prognosis, staging, and management.

The prognosis for a bladder lipoma is excellent, and after transurethral resection of the tumor, there have been no documented reports of recurrence. As stated above, resolution of symptoms usually occurs. Our case highlights the importance of keeping a wide differential for bladder masses. Even though bladder malignancy should be suspected until ruled out, rare cases of non-malignant lesions exist, such as in this case of a bladder lipoma. The timely identification and diagnosis of this mass as a bladder lipoma led to our patient avoiding any further interventions and prompt clearance for receiving a renal transplantation successfully.

4. Conclusions

Bladder lipomas are an uncommon finding among patients presenting with a bladder mass. To date, there is a paucity of literature on bladder lipomas and it is mainly limited to case reports. The presentation for a bladder lipoma can vary from asymptomatic to hematuria or LUTS. Bladder lipomas are often incidentally discovered on imaging or cystoscopy, and treatment is through resection, including TURBT. The prognosis for a bladder lipoma is excellent, and no cases of recurrence have been demonstrated in the available literature. The timely diagnosis of a bladder lipoma prevents unnecessary interventions, including repeat TURBT, follow-up cystoscopy, or other additional imaging studies, which may contribute to cost and patient uncertainty about diagnosis. However, it is important to keep a differential diagnosis, which includes more malignant conditions, such as liposarcoma and pelvic lipomatosis. Despite the overall rare occurrence of non-malignant bladder tumors, our case highlights the importance of maintaining bladder lipoma on the differential and adds to the scarce literature on the topic.