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Neuroradiology Case of the Week
Case 436
August 2009
Lisa Siripun, MD and P-L Westesson MD, PhD, DDS
Clinical
Presentation: Patient is a 26-year-old male on hemodialysis with a history of end-stage renal disease who presented with new onset seizure.
Imaging Findings: See below.
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Figure 1: There is diffuse extensive thickening of the skull with multiple well-defined lytic lesions.
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| Figure 2: Diffuse thickening of the skull and bilateral mandibles. |
Diagnosis: Renal osteodystrophy
Discussion: Renal osteodystrophy is a global term applied to all pathologic features of bone in patients with renal failure. The primary retention of phosphate by abnormal kidneys results in hyperphosphatemia, which causes hypocalcemia, resulting in secondary hyperparathyroidism.
Roentgenographic changes of renal osteodystrophy are more likely to be seem in patients who have been receiving dialysis for a long time. Short, more frequent dialysis treatments and careful control of serum calcium and phosphate levels may slow or reverse the process of renal osteodystrophy. Subsequently, there are two major types of metabolic bone disease: 1) high-turnover osteodystrophy (increased bone resorption and formation) and 2) low-turnover or aplastic disease.
Whether primary, secondary, or tertiary, hyperparathyroidism is usually diagnosed by laboratory tests long before abnormal calcium metabolism results in macroscopic skeletal changes. The various skeletal changes include generalized demineralization, subperiosteal resorption, bone cysts, and pathologic fractures. Pathognomic radiologic findings include the loss of the dental lamina, thinning of cortical bone in multiple locations (distal phalanges, distal clavicles, distal ulna, inferior margin of femoral neck and pubis, and medial proximal tibia), a coarsened trabecular pattern, and a “salt-and-pepper” appearance of bone, particularly the skull.
Skull with facial skeletal changes associated with hyperparathyroidism assume three radiographic patterns.
- The classic form is termed “osteitis fibrosa cystica” and presents with a combination of increased bone cell activity, peritrabecular fibrosis, and cystic brown tumors. Radiographically, this appears as a constellation of cortical thinning of multiple bones, coarsened trabecular patterns, osteolytic lesions, and “salt-and pepper” appearance of the skull, which is the result of mixed osteolytic and sclerotic bone.
- The second form resembles fibrous dysplasia, with a classic ground glass pattern on both conventional films and CT. Unlike true fibrous dysplasia, these findings can be diffuse and generalized, with poor corticomedullary distinction, an imaging finding not present in fibrous dysplasia.
- The third and rarest form is uremic leontiasis ossea as seen. Uremic leontiasis ossea is characterized by significant hypertrophy of the jaws with serpiginous “tunneling” or channeling within the bone and poor visualization of the cortical bone. The cause of this unusual structure is not known; no specific patterns of microscopic changes explain the radiographic findings.
All manifestations of the disorder regress with successful renal transplantation, although the changes associated with hyperparathyroidism may not recede for several months. Anticipation of renal osteodystrophy and screening radiographs of the usual sites of early involvement (i.e., the hands) allow early intervention and spare the patient the morbidity of late complications.
References:
- Kline, MJ. Osteomalacia with renal osteodystrophy. E-medicine, Nov. 27, 2007. http://emedicine.medscape.com/article/392997-overview
- Chang JI, Som PM, Lawson W. Unique imaging findings in the facial bones of renal osteodystrophy. AJNR Am J Neuroradiol. 2007 Apr;28(4):608-9. PMID: 17416805 [PubMed]
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