Fibrous dysplasia is a developmental abnormality caused by excessive proliferation of immature spindle-cell fibrous tissues in bones. It is characterized by benign bony growths, which can lead to local swelling, bony deformities, and lytic conversion, predisposing the bone to pathologic fractures. Although this process can occur in cortical bone, it primarily affects the trabecular bone, leading to enlargement and expansion from within the medullary space. Malignant transformation to osteosarcoma or fibrosarcoma can occur, although this is exceedingly rare (<0.5%).1,2
This case report describes a patient who presented with an expansile lytic mass in a lumbar transverse process that was postoperatively identified on pathology as monostotic fibrous dysplasia. Such lesions that involve the transverse processes are rare and have been associated with pain and significant discomfort.3-5 This is the first reported case of a transverse process fibrous dysplasia causing urinary retention and neurologic symptoms simultaneously. The patient provided written informed consent for print and electronic publication of this case report.
Case Report
History
A 52-year-old black man presented to us with 6 to 8 months of increasing right flank pain, difficulty with urination, and right lower extremity pain in the area of his anterior thigh. He also complained of “buckling” of his thigh with ambulation. On review of systems, the patient denied any fevers, chills, headache, changes in weight or vision, or hearing problems. He had no systemic symptoms except for 6 months of frequent urinary tract infections and difficulty emptying his bladder, which resulted in urinary retention. He denied any significant medical history and denied any use of alcohol or tobacco.
Physical Examination
On physical examination, the patient was a well-appearing 52-year-old man in no apparent distress. No signs of gross deformity, erythema, ecchymosis, or infection were noted upon examination of his lower extremities. His motor examination was within normal limits from L2 to S1. However, both fine and gross sensation were decreased in the L3 distribution. Sensation was intact to the remaining nerve-root distributions. The Babinski sign was negative for both lower extremities, and clonus was within physiologic limits. Examination of his gait was notable for quadriceps buckling with ambulation.
Radiographic Examination
The patient initially presented to his primary care physician, who evaluated his symptoms with a computed tomography scan of his abdomen and pelvis. This showed a mass of the right L3 transverse process (Figure 1). The patient was referred to us for further management of this lesion. Dedicated magnetic resonance imaging of his lumbar spine was performed, showing an expansile, lytic, homogeneous mass in the patient’s right L3 transverse process. The mass showed a significant mass effect, compressing the exiting nerve roots and, presumably, his right ureter (Figure 2). A bone scan showed monostotic disease. The patient had failed conservative management, including physical therapy and anti-inflammatory medications. His right-sided radiculopathy was worsening, and he complained that the pain was affecting his quality of life and limiting his performance of his daily activities. A pain management specialist was requested to better manage his pain. Considering progression of his condition, surgical management was discussed, leading to a planned biopsy and resection of the mass.
Surgical Procedure
The patient was taken into the operating room and positioned prone on a Jackson table with a Wilson frame. Fluoroscopy was used to localize the right L3 transverse process. An incision was made over the right L3 transverse process and a Wiltse intramuscular approach was performed. After the right L3 transverse process was identified, the soft tissue from the transverse process was retracted in all directions, including medially up to the pedicle. The intertransverse ligament was detached from both the cephalad and caudal edges of the transverse process. We used a Woodson elevator to perform subperiosteal dissection to remove the soft tissue circumferentially. After dissection, we placed a Cobb elevator to protect the rostral and caudal soft tissue and used a high-speed burr to amputate the lytic transverse process at its base. The transverse process was removed en bloc (Figure 3) and sent for frozen pathologic evaluation (Figure 4). After the diagnosis of a benign lesion, the wound was closed in layers.
Complete resolution of both urinary and neurologic symptoms were immediately noted and up to 1 month postoperatively.
Discussion
Primary bone tumors of the spine are rare, with a reported incidence of 2.5 to 8.5 per 100,000 people per year.6 The estimated incidence of benign primary tumors involving the spine accounts for about 1% of all primary skeletal tumors and nearly 5% for malignant tumors.7-9 In contrast, secondary tumors involving the bony spinal column are relatively common. Postmortem studies indicate up to 70% of cancer patients demonstrate axial skeletal involvement.10,11 The most commonly encountered benign tumors affecting the spine include giant cell tumors, osteoid osteomas, osteoblastomas, and hemangiomas. Chordomas are frequently reported as the most common malignant primary spine neoplasms. Of all primary benign bone lesions, fibrous dysplasia accounts for approximately 1.4%.8