Heterotopic Ossification Leading to Ureteral Obstruction Resulting in Nephrectomy

Abstract

Background: Heterotopic ossification (HO) is the presence of bone in soft tissue where bone normally does not exist. This can be acquired or inherited with the acquired form most often seen with either trauma, spinal cord injury, or central nervous system injury. HO most commonly affects the flexors and abductors of the hip, medial knees, and the shoulders and rarely affects the genitourinary (GU) system.

Case Presentation: We discuss a 67-year-old Caucasian male patient who presented with left-sided ureteral obstruction. He was involved in an airplane accident in 2001 resulting in a spinal cord injury. This ultimately led to heterotopic bone growth within the retroperitoneal space involving the left psoas muscle and encasing the ureter. Owing to the ureteral obstruction, a nephrectomy was performed to treat the patient's urinary symptoms.

Conclusion: Although HO is relatively common after spinal cord injuries and trauma, it rarely infiltrates the GU system. Management ultimately involves treating the symptoms that arise because of the complications from the abnormal bone formation. For this case, because of extensive ossification resulting in obstruction of the ureter and inability to separate the kidney from the psoas, the ultimate outcome was a nephrectomy.

Introduction and Background

Heterotopic ossification (HO) is the presence of abnormal bone formation in nonskeletal sites such as muscle, tendons, or other soft tissue. The most common sites of HO include the flexors and abductors of the hip, medial knee, and the shoulders.¹ HO can be inherited or acquired that is further divided into neurogenic, thermal, or traumatic. Neurogenic HO occurs after a spinal cord injury or traumatic brain injury; thermal HO occurs after a burn and correlates with total surface area burned; and traumatic HO occurs after explosive, penetrating, or blunt type injuries.¹ The process of HO is initiated by tissue trauma, ischemia, or activation of pluripotent mesenchymal cells. The exact pathophysiology has not yet been determined but there are three essential components needed for HO to occur: activation of pluripotent cells, molecular signals causing the cells to differentiate, and a suitable microenvironment for bone formation.¹

Nongenetic HO classically presents in young adults with a clear history of local trauma or surgery. A history of trauma is the initiating event in up to 75% of cases.¹ HO is uncommon in the genitourinary (GU) tract with literature review showing <10 case reports.

Treatment of HO requires a multimodal approach and is noted to be the superior treatment.¹ Early treatment involves physiotherapy and initiation of nonsteroidal anti-inflammatory drugs and bisphosphonates, radiation is used to prevent continued deposition, with the only definitive treatment being surgical excision.¹

In this study, we report a case of HO of the ureter that ultimately required nephrectomy.

Presentation of the Case

Preoperative course

The patient is a 67-year-old male with a history of spinal cord injury with L3 vertebral body fracture. He struggled with mobility, chronic back pain requiring morphine pump, and spinal cord stimulator. Owing to worsening bilateral radicular pain with left flank pain, a CT was obtained, which showed bony growth into the vertebral canal with ossification of the retroperitoneal space appearing to involve the left ureter at the level of lower pole with hydroureter to the level of the obstruction (Fig. 1). Owing to the pain and concern for ureteral obstruction, the patient underwent nuclear medicine renal imaging, which confirmed left obstructive uropathy. Split function was noted to be 48.8% on left with delayed drainage and minimal response to Lasix with a peak at 16.46 minutes (Fig. 2). Because of these findings of obstruction with preserved renal function, the patient was managed conservatively.

FIG. 1.

Coronal CT showing HO of the left psoas muscle (blue) and ureter (yellow). HO, heterotopic ossification.

FIG. 2.

Renal MAG3 scan showing that split function of the kidneys was 48.8% on the left and 51.2% on the right (yellow bracket) with minimal response to Lasix and delayed drainage on the left (blue arrow).

The patient continued to experience left flank pain, therefore, a percutaneous nephrostomy tube was placed, which resolved the left flank pain. With resolution of pain, various treatment options for ureteral obstruction were discussed including chronic indwelling stent, ureteral reconstruction, nephrectomy, and autotransplant. Chronic indwelling stent was determined to be a less desirable choice because of the extensive ossification and risk for stent failure, causing obstruction. After discussion, the patient wanted to avoid the complications of ureteral reconstruction associated with his spinal hardware. Autotransplant was discussed, but the risk of loss of the autotransplanted kidney was too great. He desired a nephrectomy and the kidney to be donated for transplantation.

Because of this, he underwent preoperative evaluation by the transplant team for which he was deemed an appropriate candidate. Further evaluation of the specimen was to be performed by the transplant surgeon at the time of nephrectomy. This perioperative evaluation by the transplant surgeon would determine whether this kidney would be appropriate for transplantation. For those reasons, we planned to perform a hand-assisted laparoscopic left simple nephrectomy.

Operative course

The patient was placed in the modified lateral position. A Veress needle was used in a standard manner to establish pneumoperitoneum. A 12 mm trocar was placed in the periumbilical incision. A hand port was placed along the midline in preparation for donor nephrectomy. A 12 mm assistant port was placed in the left lower quadrant taking care to avoid patient's morphine pump in his left abdomen (Fig. 3).

FIG. 3.

Axial CT urogram in delayed phase showing the location of the left ureter (green) as well as the HO (red) in the retroperitoneal space. You can also see all of the hardware in the lumbar spine (yellow) as well as his morphine pump (blue).

The left colon was mobilized medially in a standard manner. The mesentery of the descending colon and sigmoid were densely adherent to the left retroperitoneum. The plane between the mesentery and Gerota's fascia was developed with general surgery assistance to ensure preservation of the vasculature. Then we began the posterior dissection. The heterotopic bone formation made dissection of the kidney tedious. We were unable to separate the kidney from the psoas as the fat plane was scarred. This dissection resulted in injuries to the kidney and we were unable to lift the posterior plane to gain length on the vessels. The kidney transplant team assessed the kidney and determined that it would not be acceptable for donation. The gonadal vein was identified and used to identify the renal hilum, allowing staple ligation of the artery and vein.

Dissection continued superiorly, allowing the adrenal to be spared. The gonadal vein was then clipped and ligated. Hemostasis was ensured and Surgicel and Floseal were applied. The specimen was removed through the hand port. The fascia was closed with interrupted sutures. The skin was closed with running subcutaneous sutures and skin glue was placed superficially. He was extubated and taken to recovery.

Postoperative course

There were no complications with recovery postoperatively. His left flank pain resolved and he is happy with the outcome. His creatinine most recently was 0.94 from his baseline preoperatively of 0.99–1.19.

Discussion and Literature Review

This is an interesting case because HO does not often involve the GU tract, which makes studying this and having a standard protocol to manage GU HO difficult. We want to present basic information on HO and HO in the GU tract, as well as a workup that we feel fully evaluated the patient, allowing us to perform an appropriate treatment.

There are few published articles on the management of HO of the GU tract. Documented cases of management have varying treatments, ranging from autotransplantation² to nephrectomy.³ Stenting and ureterolysis for HO have not been documented in the literature. A man presented with a calcified ureter and underwent partial nephrectomy.⁴ Another case presented with hydronephrosis and worsening kidney function with calcification in the ureter and kidney, ultimately requiring a radical nephrectomy and ureterectomy.³ With the paucity of literature on management of HO of the GU tract, one has to rely on sound clinical judgment and experience to manage this problem.

This case taught us that HO should always be included on a differential in patients with a family history of HO or an injury that predisposes them to HO. Also, HO is a difficult diagnosis to treat and manage. One should discuss all options with patients and should generally start with conservative management. Based on this patient's desires, we elected to perform a nephrectomy for possible transplant, as he felt the risk of loss of the kidney during autotransplant was too great and preferred to donate the kidney. Unfortunately, with difficulty in dissection, the kidney was not able to be used for transplant. Our case shows that HO will likely complicate surgery and make typical dissection planes difficult to utilize, increasing the risk of intraoperative complications.

Moving forward, we now have a firsthand understanding that HO of the GU tract will make surgeries on the GU tract substantially more difficult. With this information, one must have a thorough surgical plan and have a low threshold for converting to improve exposure. In the future in patients with HO involving the ureter, we would ensure to emphasize the increased risk of the procedure. Retrospectively if autotransplantation would have been attempted, the kidney would have likely not been safe for autotransplant because of the injuries during dissection. Therefore, autotransplant may have an increased risk of loss of kidney when compared with other indications for autotransplantation.

Conclusion

In conclusion, this is a rare case of HO infiltrating into the GU system through the left ureter. Because of the extensive ossification resulting in obstruction of the ureter and inability to separate the kidney from the psoas as well as the need for subsequent neurosurgery, a nephrectomy was ultimately decided as the best treatment option. A laparoscopic hand-assisted left simple nephrectomy was performed allowing for alleviation of the obstruction.

Abbreviations Used

CT

computerized tomography

GU

genitourinary

HO

heterotopic ossification

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Cite this article as: McMahon A, Stormont G, Boyle SL (2020) Heterotopic ossification leading to ureteral obstruction resulting in nephrectomy, Journal of Endourology Case Reports 6:4, 287–290, DOI: 10.1089/cren.2020.0036.