Radiographic/CT findings

HOA is characterized by a symmetric periosteal reaction on radiographic examination (Fig. 1 Fig. 2). This periosteal reaction classically occurs in the long bones such as the tibia, fibula, radius and ulna, although a similar reaction may also occur in the phalanges (Fig. 2). In the long bones the diaphysis is typically affected first, with involvement of the metaphysis and epiphysis indicating progression of disease. Likewise, the thickness of the reaction is also an indication of advanced disease. There is typically no abnormality of the marrow or soft tissue adjacent to the periosteal reaction of HOA, and involvement of these tissues should suggest the possibility of other diagnoses [1]. In addition to the periosteal reaction described above, radiographic examination may reveal acroosteolysis or tuft hypertrophy of the digits, though these findings are much more rare (Fig. 3) [3]. In joints, HOA classically produces soft tissue swelling without joint space narrowing, erosions, or other arthritic changes. CT findings of HOA are analogous to radiographic findings (Fig. 2) and have the added benefit of potential detection of the underlying disease process causing secondary HOA [1].

Bone scintigraphy findings

Classic findings on radionuclide bone scan include dense, linear radiotracer uptake along the long bones (Fig. 4). The tibia, fibula, radius, and ulna are the most often affected and the increased uptake is most often bilateral and symmetric. Unilateral involvement is much more rare in HOA and suggests an alternate diagnosis. While the long bones are the most commonly affected, HOA can also affect the phalanges and metacarpals with resultant bone scintigraphy changes (Fig. 5). Increased periarticular uptake may also occur as a result of synovitis (Fig. 4) [4].

MRI findings

MRI findings in HOA typically include a hypointense periosteal reaction on T1-weighted images with normal underlying bone marrow signal (Fig. 6). Soft tissue edema may also occur adjacent to this periosteal reaction, demonstrated by increased signal on fluid-sensitive sequences such as STIR and FLAIR (Fig. 6) [5].

Differential Diagnoses

Several disease entities may produce diffuse periosteal reaction similar to that of HOA. As the reaction of HOA is typically bilateral and symmetric, unilateral or asymmetric reactions should prompt consideration of alternate diagnoses. Other common causes of diffuse periosteal reaction are multifocal osteomyelitis and neoplastic disease, however unlike HOA these entities will usually cause abnormalities within the underlying marrow and adjacent soft tissue (Fig. 7). Venous stasis may also produce a periosteal reaction, though radiographic evidence of varicosities and characteristic clinical symptoms will typically be present to support this etiology (Fig. 7). In children Caffey disease and hypervitaminosis A may produce multifocal periosteal reaction, those these entities usually present at an earlier age than would be expected for primary HOA [1-2].