Ureter and Nerve Root Compression Secondary to Expansile Fibrous Dysplasia of the Transverse Process

Primary and secondary malignant osseous tumors have a predilection for the anterior column, and primary benign lesions usually affect the posterior column.^8,12-14 Because of the greater blood supply and more direct communication with the viscera via the Batson plexus, the anterior column is most likely to be seeded by metastatic disease. Similarly, hemangiomas and multiple myeloma are typically located in the anterior column, most likely because of the more abundant blood supply there. Chordomas are also found in this cancellous anterior column. Osteoid osteoma, osteoblastoma, and aneurysmal bone cysts are found within the more cortical architecture of posterior elements. The location of this patient’s lesion within the transverse process elevates confidence in the diagnosis of a benign lesion.

The conventional, isolated form of fibrous dysplasia was originally described in 1942 by Lichtenstein and Jaffe.² They described 15 cases of benign “nonosteogenic fibromas” near the ends of long bones in young patients. Monostotic fibrous dysplasia constitutes the majority of these cases, approximately 80%.^1,2,8,15 Fibrous dysplasia may also present as part of McCune-Albright syndrome, in which case it is associated with precocious puberty and café au lait spots. Less commonly, they are associated with intramuscular myxomas, as in Mazabraud syndrome. The lesions in these syndromes are typically polyostotic. In all forms, fibrous dysplasia develops from an activating mutation in the gene that encodes the alpha subunit of the G protein on chromosome 20q13, activating cyclic adenylate cyclase and slowing the differentiation of osteoblasts.^3,8

With regard to presentation, fibrous dysplasia is usually asymptomatic and discovered incidentally. The literature reports that the most common presenting symptom for patients with monostotic fibrous dysplasia of the spine is back pain localized to the lesion.¹⁵ Meredith and Healey² completed a comprehensive review of 54 cases of monostotic fibrous dysplasia involving the spine in which the majority of symptoms included back pain, neck pain, sacral region pain, pathologic fracture, painful torticollis, progressive myelopathy, paresthesias of the foot, and only 1 case of radiculopathy involving thoracic vertebra. In normal anatomy, the ureter lies within retroperitoneal fat anterior to the psoas muscle and L2-L5 transverse processes and is normally mobile.^16-18 This becomes clinically significant in lean patients as the ureter becomes closer to the spine. There are several reports of iatrogenic ureter injury in lumbar disc surgery.^16-18 Normal variants, including medialization towards the spine, may predispose the ureters to injury, iatrogenic, or otherwise. In fact, medialization of the ureters occurs commonly in black men and usually involves the right side, which may have occurred in this black patient.¹⁹

Fibrous dysplasia is most often diagnosed by its radiographic appearance or biopsy. However, recent data suggest that deoxyribonucleic acid (DNA) analysis may soon be able to diagnose this process.²⁰ Imaging typically reveals expansile, central lytic lesions within the medullary cavity. Pathology shows dense fibroblasts around immature woven bone, commonly referred to as “Chinese lettering.” The treatment varies from observation to en bloc surgical resection. Clinical observation is warranted for asymptomatic or incidental findings of monostotic fibrous dysplasia, as long as the risk for pathologic fracture is low.¹¹ Bisphosphonate therapy, both oral and intravenous, offers promising outcomes for the treatment of fibrous dysplasia, with improvement in pain and function as well as in the radiographic findings.^11,21 Management of monostotic fibrous dysplasia presenting as an isolated expansile mass of the transverse process in lumbar spine has rarely been described.^3-5 Troop and Herring⁵ reported a case of monostotic fibrous dysplasia in the lumbar spine, with involvement of the vertebral body and the posterior elements. Chow and coauthors³ and Harris and colleagues⁴ described the involvement of the transverse process of L4. Chow and coauthors’³ treatment consisted of excision that resulted in an asymptomatic patient at 8-year follow-up, while Harris and colleagues⁴ chose observation. In the latter study, the patient’s lower back pain persisted at 4-year follow-up.

Progressive enlargement, recurrence, and malignant transformation have all been described. Meredith and Healey² reported the reappearance of monostotic fibrous dysplasia affecting C2, extending through the fusion mass to involve a previously unaffected vertebra 20 years after the original C2 posterior elements excision via posterior spinal fusion from C1 to C3. In the literature, the incidence of malignant transformation ranges from 0.4% to 4%.⁸ One case of malignant transformation in thoracic spine was reported by Fu and colleagues.²² Therefore, complete removal of all affected bone is recommended.^{1,2,4,5,15,22,23}

Conclusion

We present an unusual condition with complete resolution of symptoms after surgical resection. Several points may be considered from this report. Fibrous dysplasia lesions have been found in all bones of the body, including the skull, face, and extremities; however, monostotic fibrous dysplasia involving the spine is rare.^11,23,24 Furthermore, there are no other reports of these lesions causing simultaneous nerve compression and urologic symptoms. Considering anatomy, clinicians may consider lesions of the lumbar transverse process in patients presenting to orthopedic surgeons with urinary symptoms, especially when combined with neurologic symptoms. In these lesions, fibrous dysplasia should be within the differential diagnosis. Clinicians should also recognize that complete resolution of symptoms has been reported with wide resection of these lesions.