CHAPTER 20 BENIGN BONE TUMORS OF THE FOOT AND ANKLE, Robert R. Miller, D.P.M. Stephen V. Corey, D.P.M. Benign bone tumors of the foot and ankle typically Table 1 displays the percentage of each lesion present both a diagnostic and therapeutic challenge found in the leg and foot. The lesions represent a to podiatric surgeons. These lesions have a percentage of local lesions compared to the total relatively low incidence of occuffence in the foot number of lesions reported for the studies. It does and ankle when compared to other regions of the seem apparent that the overall incidence of foot body, and the behavior of these lesions may mimic and ankle involvement is relatively low, but some malignant tumors. Not only is it impofiant to tumors do occur with a somewhat frequent rate. recognize a specific lesion to insure proper treat- Primarily, enchondroma, osteochondroma, osteoid ment, but the ability to differentiate a benign from osteoma, simple (unicameral) bone cysts, and malignant process is of utmost importance. aneurysmal bone cysts are somewhat common in It is difficult to determine the true incidence of the foot and ankle. benign bone tumors of the foot and ankle. Most large studies do not distinguish individual tarsal RADIOGRAPHIC CHARACTERISTICS OF bones, nor is there a distinction made befween BENIGN BONE TUMORS proximal and distal aspects of the tibia and fibula. Dahlin's Bone Tumors has reported findings of the Several radiographic parameters have been Mayo Clinic up until 7993.' total 2334 Of a of described to differentiate between benign and benign bone tumors affecting the whole body, malignant bone tumors. Although there are 3.3o/o involved the foot and 19 .3o/o involved the tibia exceptions to each of these parame't-ers, most lesions and fibula. total Of a of 5642 malignant bone can be differentiated by following these guidelines. tumors affecting the entire body, 7.30/o involved the None of these guidelines alone can make the foot and 12.40/o involved the tibia and fibula. diagnosis of a benign or malignant bone tumor. Table 1 SKELETAL LOCALIZAIION OF BENIGN BONE TUMORS Dahlin & Unni(1) Tibia Fibula Foot Total Lesions Enchondroma 2o/o !o/o 2o/o 748 Osteoid osteoma 79o/o 1o/ct 5o/o 332 Osteochondroma 70% 4o/o 7o/o /44 Resnick & Niwayama(2) Enchondroma 3o/o 2o/o 7o/o 7028 Osteoid osteoma 240/o 4o/o l7o/o 661 Osteochondroma 79o/o 4o/o 60/o 7604 Simple Bone Cyst 6o/o 5o/o 7o/o 884 Aneurysmal Bone Cyst 75o/o 7o/o Bo/o 40) CHAPTER 20 121 Cortical destruction is usually associated with characterizedby a margin that can be readily traced malignant lesions. Most benign lesions will have a with a pencil or ball point pen. In contrast, a well-defined, intact overlying cortex within the "wide" zone of transition or ill-defined border bone of origin. Exceptions include benign cannot readily be outlined or traced. Resnick processes such as giant cell tlrmors, aneurysmal describes three patterns of bone destruction: bone cysts, eosinophilic granulomas, and infection, geographic, moth-eaten, and permeative.a Most all of which can be associated with a variable benign bone tumors are characterized by a degree of cortical thinning and/or destruction.3 "narrow'" (geographic) zone of transition, whereas Periosteal reactions are non-specific findings malignant or aggressive benign tumors ate which can occur in response to any process which associated with a "wide" (moth-eaten or perme- irritates the periosteum. Trauma, fracture healing, ative) zone of transition. infection, as well as benign and malignant tumors, Finally, the orientation of a lesion with respect can cause periostitis. Most benign periosteal to the long axis of a long bone can help to reactions ate charucterized by a thick, dense determine a benign from malignant process. Most pattern where the affected bone has the abiliry to benign tumors of long bones will have a long axis respond to the underlying pathology. This can that is parallel to the long axis of the bone that is generally occur because most benign processes are affected. This is probably the least reliable feature slow growing and allow adequate response time of as there are numerous exceptions, and probably the bone. On the other hand, a malignant or has little to no value when evaluating tumors of the aggressive periosteal reaction is characterized by a tarsal bones. non-uniform region of bone production. Examples Table 2 lists several radiographic features that would include sunburst or lamellated periosteal can be used to help determine if a lesion appears reactions where bone production is rapid and non- benign or malignant on radiographs. No one uniform. Most benign processes are characteized feature is pathognomonic. by benign periosteal reactions, although an aggressive reaction can be seen in benign tumors ENCHONDROMA such as aneurysmal bone cysts, aggressive giant cell tumors, eosinophilic granulomas, and osteoid An enchondroma is a benign cartilage growth that osteomas.3 In general, malignant lesions will not occurs in the medullary cavity of a bone. This lesion cause benign periostitis. can occur in any bone that is preformed in cartilage. The zone of transition is the border or margin Enchondromas account for approximately 72o/o of which surrounds a lesion within the bone of origin. primary bone tumors. The lesion typically arises Helms states this is one of the most reliable during growth of the child, but does not manifest indicators of a benign versus malignant lesion.3 A symptoms until the third to fourth decade. It is the "narfow" or well-defined zone of transition is most cofirmon tumor of the small bones of the hand.' Table 2 RADIOGRAPHIC FEAIIIRES OF BENIGN AND MATIGNAIIT BONE TUMORS X-RAY EVAIUAIION BENIGN MALIGNANT cortical break fzfe extensive periosteal reaction single layer multi-layer zone of transition "nafrow" "wide" (geographic) (permeative) trabeculation COATSE fine marginal sclerosis thick thin tumor size small large overall appearance geographic moth-eaten 122 CHAPTER 20 Enchondromas are thought to represent the The radiographic features of the lesion can be most common tumor of the foot.1.56 Common sites distinct when present. The lesion is characterized include the phalanges, metatarsals, and tarsal by a central nidus (appears radiolucent) and a bones. The lesion is typically associared with pain- variable amount of reactive sclerosis. These find- less swelling unless pathologic fracture occurs. ings are usually very obvious if the lesion is present Fractures through the lesion are common. in long bones and has a cortical location. Lesions The radiographic features are by no means occurring in primary cancellous bone may not unique. Typically, a radiolucency is encountered show such distinct features. Three out of ten with a variable degree of thinning of the overlying osteoid osteomas of the foot reported by Shereff et cortex. Often, pllnctate radio-densities can be al. had normal routine radiographs, but were appreciated which represent calcification of the detected with tomography.'\7hen lesions are not matrk within the lesion. The presence of pinhead- visualized by plain radiographs, most can be to match head-sized radiopacities (reflecting calcifi- located with the use of a CT scan. cation) in the regional area helps to clinch the The mainstay of treatment seems to be diagnosis.T The tumor is most commonly located in complete surgical resection of the nidus. Often, the central to distal aspect of the phalanges and incomplete resection of the nidus may afford metatarsals. partial to total relief of symptoms.lo In order to Treatment should be aimed at the prevention adequately resect the lesion, it must first be local- of pathologic fracture, especially if the lesion is ized within the parent bone. Most often this is found in the small bones of the hands and feet. accomplished by the use of a CT scan, but other Curettage with bone grafting is the most common methods which have been described include the method of treatment. Curettage with cryotherapy is use of radioactive isotopes (such as technetium), another treatment modality. The recurrence rate and tetracycline with UV light fluorescence. after resection of the lesion is low. Surgical resection seems to be associated with an approximately 2o/o recufrence rate. Spontaneous OSTEOID OSTEOMA regression of untreated osteoid osteomas has been repofted, although no histologic confirmation was An osteoid osteoma is characterized by a central obtained in many of the cases.'n nidus that is typically less than one centimeter in size. Another distinct feature is that the nidus is OSTEOCHONDROMA usually surrounded by a variable degree of reactive sclerosis. An osteochondroma is a hyaline cartilage capped Osteoid osteomas account for approximately protrusion on the external surface of a bone. 770/o of all primary bone tumors. Most patients with Osteochondromas are the most common primary this lesion are between the ages of 10 and 25 years bone tumors and account for approximately 50o/o of old. The lesion is characterized by nocturnal all benign bone tumors. Almost any age group can pain that is frequently rapidly relieved by the be affected, although most patients will present administration of aspirin or nonsteroidal anti- with this lesion in the second to third decade. inflammatories. There is evidence that the pain may Malignant transformation has been described in be mediated by prostaglandins.' approximately 1o/o of these lesions, and should Osteoid osteomas probably represent the always be suspected if this lesion is painful. second most common tumor of the foot, with the Complications that have been described with this talr-rs being most commonly affected.6 A11 other lesion include fracture at the base of the lesion, tarsal and leg bones can be affected.