Unusual Presentation of Fibrous Dysplasia in an Elderly Saudi Patient

2018-03-21 19:17:04

Category: Musculoskeletal Imaging, Region: Pelvis-Hip joint, Plane: Coronal

Case Presentation & Clinical History: This is a 67-year-old female who is a known case of diabetes mellitus for 10 years, hypertension, dyslipidemia and ischemic heart disease with no known allergies nor recent history of infection. The patient has morbid obesity (BMI=47) and osteoarthritis with limited mobility. The patient was complaining for one month of abdominal/flank pain, generalized malaise, fullness, and lower limbs pain with a subjective weight loss and decreased oral intake. The patient, however, did not have any shortness of breath, cough, sore throat/runny nose, nor hemoptysis. CT and MRI were done at another hospital which showed large bony lesion in the right superior iliac crest. The patient was advised to have a biopsy of the bony lesion. However, she refused and signed a discharge against medical advice (DAMA) consent, and then came for follow-up to King Abdulaziz Medical City, Riyadh, Saudi Arabia. The patient was referred to orthopedic oncology services. Routine biochemical investigations were performed during the initial presentation to the emergency department, and they included hematology and tumor markers; such as Alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), cancer antigen (CA-125), and cancer antigen (CA 19.9). All biochemical investigations and tumor markers were within normal limits. -Radiological Data: The anteroposterior pelvic radiograph showed a large, expansile lesion with calcification and internal septation at the right iliac bone with no periosteal reaction or cortical breakthrough (Figure 1). The CT chest revealed small non-specific nodules bilaterally. The abdominal and pelvis CT was performed to assess the large right iliac mass lesion. The CT showed a right expansile mass lesion extending from the right iliac bone and measuring 11.6 x 12.8 x 8 cm. The lesion showed heterogenous densities with areas of septation, calcification, and heterogenous enhancement. Furthermore, there were no associated soft tissue mass lesion noted nor cortical breakthrough. The acetabulum appeared spared with relative atrophy of the muscle on the right side (Figure 2). The pelvis MRI showed a mass with well-defined borders which had no medullary or cortical continuation. It also showed no other associated soft tissue masses (Figure 3). The diagnostic considerations of that lesion are broad. However, they include plasmacytoma, giant cell tumor, and chondromyxoid fibroma. Upon taking the informed consent of the patient, an ultra-sound-guided biopsy of the right pelvic mass was performed. The procedure was performed under aseptic technique. Using coaxial technique, three passes of 16-gauge and seven passes of 18-gauge core biopsy were obtained and sent fresh and in formalin. -Pathology Results: Multiple needle core biopsies were microscopically examined. They reveal a bland fibro-osseous lesion. The osseous component appears as spicules and trabeculae of woven bone with no osteoblastic rimming (Figure 4). The fibrous component lacks significant cytologic atypia or mitotic activity. The differential diagnosis of low grade medullary osteosarcoma was ruled out based on MDM2 amplification study which was done at ARUP laboratories, Salt Lake City, Utah, USA. The MDM2 amplification came as negative with an MDM2/CEP12 ratio of 1.1. The average MDM2 signal number per cell was 1.8. Since the histomorphology was highly suggestive of fibrous dysplasia, further confirmatory PCR-based DNA sequencing for GNAS mutation limited to exon 8 (including mutation hot spot codon 201) and exon 9 (including mutation hot spot codon 227) of the GNAS gene was performed at the university of Texas MD Anderson Cancer Center Molecular Diagnostic Lab. A mutation was detected in codon 201 (CGT to TGT) in exon 8 of the GNAS gene, that would change the encoding amino acid from Arg to Cys (R201C). The Standardized nomenclature for this mutation is “NM_000516: c.601C>T p.Arg201Cys”. As such the final diagnosis of fibrous dysplasia was rendered. -Outcome & Follow-up: Four months later, interval imaging was done. The pelvis X-ray showed redemonstrations of the large, expansile lesion with internal septation at the right iliac bone with no significant interval changes seen. The pelvis MRI demonstrated a mass lesion with well-defined borders that appeared to have marked chondroid matrix. Furthermore, the mass appeared to exhibit mass effect on the surrounding soft tissues. However, the overall morphology and size appeared unchanged upon comparison to the previous study. Further interval studies up to eighteen months - which included both plain X-rays and pelvis CT - showed no significant change. Subsequent management included reassurance, clinical observation with annual clinical assessment.