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. The pain infarction of the osseous stalk, impingement of associated with the lesion is often worse with local tendons and nelves, pseudoaneurysm of weight bearing and ambulation. Clinical signs can adjacent blood vessels, and bursae formation over include pain with joint range of motion, an antalgic the tip of the lesion.'u gait, and muscle atrophy which may mimic a \7hen present in the foot, the lesions seem to neuromuscular disease or a systemic form of occur most commonly in the metatarsals, tarsal arthdtis. Most commonly, the lesion will reveal bones, and phalanges. It can also be found near localized edema and tenderness on physical the metaphyseal region of the tibia and fibula examination. about the ankle joint. Most frequently, the lesion CFIAPTER 20 123 will present as a painless mass that can be aggra- The cyst is usually found in the central aspect vated by weight bearing and ambulation. The of long bones. In the calcaneus, the lesion can be lesion is often found incidentally when routine found inferior to the posterior facet. The cortex of radiographs are obtained. the parent bone is always intact, unless fracture has The radiographic features of this lesion are occurred. A characteristic feature is the fallen unique and distinct from any other bone tumor. fragment sign. This represents a free fragment of The lesion is characterized by a "stalk" that usually cortical bone which by gravity falls to the lowest emanates from the metaphyseal region of a long portion of the cyst. The fragment can fall freely bone. The base and stalk of the lesion contain as the result of the cyst being fluid filled and cortical and medullary bone that are in direct unilocular. continuily with the bone of origin. The lesion also Curettage and bone grafting of the lesion is frequently points "away" from the joint near which the conventional method of treatment. Scaglietta et it arises. al. showed favorable results in 90o/o of patients One lesion that must be differentiated from an treated by intralesional injection of methylpred- osteochondroma is a subungual exostosis. Major nisolone acetate.l The cyst is obserued for differences include the following: opacification over the next 3 to 6 month period to evaluate for healing. Regardless of the method of A subungual exostosis does not exhibit treatment, recurrence rates have been reported as cortical or medullary continuily with the bone high as 200.0 to 5000. of origin. A subungual exostosis arises from the tip of a ANEURYSMAL BONE CYST phalanx (which is not metaphyseal bone). The cartilage cap of a subungual exostosis This lesion accounts for approximately 5o/o of consists of fibrocartilage, whereas the cap of an primary bone tumors. Nearly B0% of these lesions osteochondroma consists of hyaline caftilage. occur in patients less than 20 years of age. Of 257 cases of benign bone tumors of the foot treated at A subungual exostosis displays histologic the Bone Tumor Center of the Ptizzoli Institute, pro- features which consist of spindle cell approximately 700/o of the tumors were aneurysmal liferation. bone cysts.l' The treatment of an osteochondroma typicaliy There is some confusion in the literature as to consists of excision of the tumor flush with the whether this is a primary or secondary lesion. Some bone of origin. Not all lesions need to be resected, authors believe that the tumor is a primary lesion entity, whereas but indications would include pain or disability, an that arises as ^n independent abnormal increase in size or pain, or radiographic others believe the lesion arises from another features that suggest malignancy. Resection has pre-existing lesion. Two lesions which seem to been associated with an approximately 20/o commonly give rise to an aneurysmal bone cyst fecurfence fate. include giant cell tumors and chondroblastomas. Pain and swelling of varying duration are the STMPLE (UlVrCeUERAr) BONE CYST most common presenting symptoms. Lesions which are in close proximity to joints may cause Simple bone cysts are fluid-filled solitary cysts that pain with joint motion or even an apparenl typically arise in the metaphyseal region of long synovitis. Pathologic fracture is common. bones. These lesions are most frequently seen Aneurysmal bone cysts often show rapid enlarge- in the femur and humerus of children and ment during pregnancy. adolescents. In adults the lesion is most commonly Plain radiographs often reveal a metaphyseal found in the calcaneus and ilium. The lesion is lesion located in an eccentric position. Cortical rarely symptomatic unless pathologic fracture has thinning and osseous expansion are frequently occurred. Often the lesion will produce mild and noted features. Fluid-fluid levels are characteristic vague symptoms, but attention is usually directed and seen on both CT scans and MRI. The fluid-fluid to the lesion as a result of minor or incidental levels represent loculated areas within the cyst that trauma. contain degraded blood products, serum, and tumor fluid. 124 CI]APTER 20

The most successful treatment reported by REFERENCES Dahlin has been surgical removal of the entire lesion, or as much of it as possible.' Bone grafting 1. Dahlin D, Unni KK: Bone Tumors, General A$)ects and Data on 1.1,087 Cases,5rh ed, Philadelphia, PA: Lippincott-Raven; L996. of the resultant defect may be required. Curettage 2. Resnick D, Niwayama G:Diagnosis of Bone and Joint Disorders, with cryotherapy and en bloc resection have also Vol. 6, Philadelphia, PA: W.B. Saunders; 1988. 3. Helms CA:Malignant Bone and Soft Tissue Tumors. In been described. Excision of the lesion is associated Furulamentals of Diagnostic RadiologtBaltimore, MD: \7i11iams & with a 70o/o to 30o/o recurrence rate. \(zilkins: 1994. Resnick D:Tumors and Tumor-1ike Lesions of Bone: Radiographic Principles. In Bone c1n(l Joint Imaging, Philadelphia, PA: W.B. SUMMARY Saunders; 1!89. 5. Shajowicz F: Tumors and TumorJike Lesions of Bone andJoints New York, NY:Springer-Verlag; 1981. Recognition of benign bone tumors of the lower 6. Steiner GC: Neoplasms of tbe Fctot and Leg, Baltimore, MD: 'Williams extremity is afi important skill for podiatric & Y/ilkins; 1990. 7. Jaffe HL: Atlas of Bone Patholog,t With Clinical and Racliograpbic surgeons. Not only is it important to be able to Corelations, Philadelphia, PA: J.B. Lippincott; 1992. recognize individual benign bone tumors, but it is 8. Gitelis S, Wilkins R, Conrad EU:Benign bone tufi1ors. J BoneJoint Surg 77 A:77 56-17 82, 1995. also very important to be able to distinguish benign o Shereff MJ, Cullivan W'T, Johnson KA:Osteoid Osteoma of the from malignant lesions. Treatment and appropriate foot, J Bone Joint Surg 65$38-641, 1983. 10. Huvos AG :Bone Tumors: Diagnosis, Treatment, and Prognosis, referral of bone tumors is based on the ability to Philadelphia, PA: W.B. Saunders; 1991. recognize the lesion, an understanding of current 11. Casadei R, et al.:Aneurysmal bone cyst and giant ce1l tumor of the toot, Foot Ankle 77487-495, 1995. treatment methods, and the skills of the surgeon.