DOI: 10.1148/radiol.2211991689
(Radiology. 2001;221:199-200.)
© RSNA, 2001
The Blade of Grass Sign1
Keith Wittenberg, MD
1 From the Department of Diagnostic Radiology, Mayo Clinic and Foundation, Rochester, Minn. Received September 14, 1999; revision requested October 26; revision received November 18; accepted December 13. Address correspondence to the author, St Paul Radiology, 250 Thompson St, St Paul, MN 55102 (e-mail kwittenberg@stpaulrad.com).
Index terms: Femur, abnormalities, 444.84 • Osteitis deformans, 444.84, 456.84 • Signs in Imaging • Tibia, abnormalities, 456.84
 |
APPEARANCE
|
|---|
The blade of grass sign, also known as the flame sign, represents a wedge- or V-shaped area of radiolucency typically located in the diaphysis of a long bone (Fig 1).
View larger version (84K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1. Lateral radiograph of the distal femur reveals a wedge- or V-shaped area of radiolucency in the diaphysis (arrows); this lucency represents the blade of grass sign and is indicative of active Paget disease. Above this osteolytic region, the bone is slightly expanded and has a coarsened trabecular pattern.
|
|
|
EXPLANATION
|
|---|
The blade of grass sign is characteristic of Paget disease of bone. Early in the disease course, the area of osteolysis that occurs in the diaphysis of the tibia or femur appears wedge-shaped and produces the blade of grass sign. When there is calvarial involvement, the area of osteolysis appears more rounded and is termed osteoporosis circumscripta. Osteolytic changes may also be seen in Paget disease in the pelvis and spine.
|
DISCUSSION
|
|---|
Paget disease (osteitis deformans) is a common disease of bone characterized by an increase in osteoclast-mediated bone resorption and accompanied by a compensatory increase in bone formation. The exuberant bone remodeling results in a disorganized, structurally weakened mosaic of woven and lamellar bone (1). Although the cause of Paget disease remains unproven, results of recent studies have suggested that both genetic and viral factors may play a role (2). It is most often asymptomatic and encountered as an incidental finding. In symptomatic patients, the most common complaint is pain while at rest, which may be exacerbated by the patient bearing weight. Biochemical markers, such as serum bone-specific alkaline phosphatase and urinary hydroxyproline, may be useful adjuncts in establishing the diagnosis and assessing response to therapy (3).
Although Paget disease may affect any portion of the skeleton, changes are seen predominantly in the axial and proximal appendicular skeleton in approximately 80% of cases. The most commonly affected sites are the pelvis (and sacrum), lumbar spine, femur, tibia, and skull. Other sites that may be involved include the clavicles, scapula, ribs, and facial bones. The hands and feet are rarely affected (4). Paget disease is polyostotic in most cases but may be monostotic in 10%–35% of cases (5).
Musculoskeletal complications of Paget disease include bowing deformities with secondary arthritis, insufficiency fractures, nerve compression (particularly with calvarial or spinal involvement), and malignant degeneration. When Paget disease undergoes malignant transformation, the most common secondary sarcoma is osteosarcoma, although other malignant tumors have been reported. The precise risk of malignant degeneration is unknown but may be as high as 5% in those with extensive skeletal disease (6). Development of an area of osteolysis that is not flame-shaped in a patient who has known Paget disease and increasing pain may suggest the presence of malignant degeneration. Insufficiency fractures are also a common complication of Paget disease (7) and often involve the femur and tibia. These fractures appear as horizontal lucencies that arise from the convex surfaces of the bone (in contradistinction to osteomalacia, in which they arise from the concave surfaces).
Paget disease progresses through three phases of remodeling: (a) an early, osteolytic phase, (b) an intermediate or mixed phase, during which increased resorption is seen in combination with increased new bone formation, and (c) a late or sclerotic phase. Each phase has a distinctive radiographic appearance that is usually sufficient to establish the diagnosis of Paget disease. Most often, affected bones demonstrate a coarsened trabecular pattern and cortical thickening that encroaches on the medullary cavity (Fig 2). While Paget disease in the long bones demonstrates a predilection for epiphyseal involvement, the characteristic osteolytic changes most commonly involve the diaphyses (8). Vertebral bodies may demonstrate a coarsened trabecular pattern with peripheral areas of sclerosis and squaring, resulting in the so-called picture frame appearance.
View larger version (77K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2. Anteroposterior radiograph of the proximal femur in the same patient depicts diffuse, mixed osteolytic and sclerotic changes with cortical thickening that narrows the medullary cavity. These changes extend to the proximal femoral epiphysis and are characteristic of the intermediate or mixed phase of Paget disease.
|
|
Magnetic resonance (MR) imaging and bone scintigraphy are useful adjuncts in the evaluation of Paget disease. Bone scintigraphy is the most sensitive means of determining the extent of disease. Areas of Paget disease appear as sites of markedly increased tracer uptake and may precede changes seen at radiography, particularly during the active phase of the disease. Rarely, however, during the inactive phase of the disease, results of bone scintigraphy may sometimes appear false-negative because of the decreased bone turnover associated with this phase of the disease (9). The exact role of MR imaging in the detection of Paget disease is less established, but it may be used in patients with changes in the nature or extent of their pain to exclude the possibility of a fracture or malignant degeneration (10).
The treatment of Paget disease has evolved dramatically over the past 3 decades with the advent of potent inhibitors of osteoclast-mediated bone resorption (11). Clinicians can now control pagetic symptoms and achieve clinical remission. Studies have shown that reduction in bone turnover is associated with signs of clinical, biochemical, and radiographic improvement. By controlling the activity of Paget disease, its natural progression may be altered with a resulting decrease in the incidence of complications.
|
FOOTNOTES
|
|---|
A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
|
REFERENCES
|
|---|
-
Tiegs RD. Paget’s disease of bone: indications for treatment and goals of therapy. Clin Ther 1997; 19:1309-1329.[CrossRef][Medline]
-
Siris ED. Paget’s disease of bone. J Bone Miner Res 1998; 13:1061-1065.[CrossRef][Medline]
-
Alvarez I, Guanebens N, Peris P, et al. Discriminative value of biochemical markers of bone turnover in assessing the activity of Paget’s disease. J Bone Miner Res 1995; 10:458-465.[Medline]
-
Resnick D. Paget’s disease of bone: current status and a look back to 1943 and earlier. AJR Am J Roentgenol 1988; 150:249-256.[Free Full Text]
-
Siris E, Kelsy J, Flaster E, et al. Paget’s disease in the United States: a survey of 700 patients (abstr). J Bone Miner Res 1988; 3:S93.
-
Schajowicz F, Santini Araujo E, Berenstein M. Sarcoma complicating Paget’s disease of bone: a clinicopathological study of 62 cases. J Bone Joint Surg Br 1983; 65:299-307.
-
Nicholas JA, Killoran P. Fracture of the femur in patients with Paget’s disease. J Bone Joint Surg Am 1965; 47:450-461.[Abstract/Free Full Text]
-
Resnick D, ed. Diagnosis of bone and joint disorders 3rd ed. Vol 4. Philadelphia, Pa: Saunders, 1995; 1396.
-
Wellman HN, Schauwecker D, Robb JA, Khairi MR, Johnston CC. Skeletal scintimaging and radiography in the diagnosis and management of Paget’s disease. Clin Orthop 1977; 127:55-62.
-
Kaufman GA, Sundaram M, McDonald DJ. Magnetic resonance imaging in symptomatic Paget’s disease. Skeletal Radiol 1991; 20:413-418.[Medline]
-
Siris ED. Paget’s disease of bone. In: Favus MJ, eds. Primer on metabolic bone diseases and disorders of mineral metabolism. 3rd ed. Philadelphia, Pa: Lippincott-Raven, 1996; 406-419.
This article has been cited by other articles:
|
|
|
|
 
S. E. Smith, M. D. Murphey, K. Motamedi, M. E. Mulligan, C. S. Resnik, and F. H. Gannon
From the Archives of the AFIP: Radiologic Spectrum of Paget Disease of Bone and Its Complications with Pathologic Correlation
RadioGraphics,
September 1, 2002;
22(5):
1191 - 1216.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
APPEARANCE
EXPLANATION
