Radiology Corner – An Expansile Lesion of the Finger

By: Terry R. Yochum, DC, DACBR, Fellow, ACCR, Michael S. Barry, DC, DACBR, and Chad J. Maola, DC

History

This adult male patient complains of chronic pain in the finger with an enlarging mass. What is your diagnosis?

Figure 1. Finger with enlarging mass.

Figure 1. Finger with enlarging mass.

Diagnosis

Malignant degeneration of a previously benign solitary enchondroma.

General Considerations 

Solitary enchondroma is a common benign bone tumor arising in residual islands of cartilage left in the metaphysis as the physis grows away. It appears as a single lesion within the interior of the bone with a great predilection for the bones of the hand and foot, although it may occur in any bone preformed in cartilage. It is often found by the coincidence of trauma, since most lesions of the hand are asymptomatic, unless pathologic fracture occurs secondary to structural weakening. It is also called a central chondroma.

Incidence 

Solitary enchondroma represents the most common benign bone tumor of the hand.It comprises 10% of all benign bone tumors.The second most common tumor of the hand that secondarily affects bone is pigmented villonodular synovitis.3

Clinical Features 

Age and sex distribution. The tumor arises during the growth period, and most tumors are seen between the ages of 10 and 30; peak incidence is usually in the third decade. Males and females are equally affected.

Signs and symptoms. The most frequent mode of presentation is that of a painless tumor, which is found in the hands and feet. Since the lesion has been present for an extended period of time before it creates any symptoms, the duration of symptoms is short. A pathologic fracture following some trivial trauma usually precipitates localized pain and swelling. Many patients live a normal life span with an enchondroma in the hand or foot and never develop any symptoms or even take notice of its presence.

Lesions affecting the long tubular bones (femur and humerus) may also be asymptomatic, but enchondromas in these locations tend to be more symptomatic than those of the small tubular bones of the hands and feet. Sudden onset of pain without any history of trauma may indicate active growth and herald the onset of malignant degeneration, an event that occurs much more frequently in long, bone enchondromas than in the short tubular bones of the hands and feet.4

Location. Approximately 50% of all enchondromas occur in the small tubular bones of the hand, with the phalanges accounting for 40% and the metacarpals 10%.Only rarely is the thumb affected.Enchondromas occur more commonly on the ulnar than on the radial side of the hand.In the phalanges the tumor is near the proximal end and in the metacarpals toward the distal end.The proximal phalanges, distal metacarpals, and middle and distal phalanges are the involved areas, in decreasing order of incidence. Occasionally, the foot will be involved. Other sites include the femur (14%), humerus (13%), and ribs (13%).The malignant potential of enchondroma increases dramatically the closer the lesion is to the axial skeleton.4,7 Enchondromas have been documented within the patella.Tumors of the patella are uncommon; however, when present they are usually benign and of cartilaginous origin. Other obscure sites documented are the mandible,skull base,10 and vertebrae.Flat bones, such as the pelvis and sternum, are only rarely involved and carry a high potential for malignant degeneration.5

Pathological Features 

The gross characteristics are rarely evident in surgical specimens since the standard form of treatment is curettage of the lesion, and all that is received are small granules or ricelike fragments of cartilaginous material, sometimes embedded in spicules of bone, where the tumor abuts on the surrounding normal tissue. Histologically, the tumor is composed of small masses or nodules of hyaline cartilage, separated by a scant, sometimes richly vascularized fibrous stroma. Foci of calcification are sometimes encountered in the cartilage; this occurs in approximately 50% of the cases and can be seen on radiographs. All tumors of cartilage matrix have a great predilection for calcification, including other cartilaginous tumors such as osteochondroma and chondroblastoma. It is often very difficult to differentiate enchondromas from malignant cartilage tumors histologically. Correlation with the clinical and radiographic data is absolutely necessary in order to avoid an incorrect diagnosis and needless surgery.

Radiologic Features 

Enchondroma presents as a geographic area of radiolucency that expands and may deform bone. The margins are well defined. The cortex remains intact, although it may be considerably thinned because of endosteal scalloping and expansion. Most singular lesions are centrally placed, within the metaphysis; however, the occasional eccentric lesion is noted, which may create quite a large mass. Stippled or punctate matrix calcification is found scattered randomly throughout the lucent defect in 50% of cases. Without such calcification enchondroma must be differentiated from fibrous dysplasia, unicameral bone cyst, chondroblastoma, giant cell tumor, and osteoblastoma. If the lesion is placed in the distal phalanx, an epidermoid inclusion cyst or glomus tumor is the prime differential consideration. Epidermoid inclusion cyst represents post-traumatic implantation of epidermoid tissue within the bone. This cyst is found most often in patients who do a lot of sewing and who are likely to have needles penetrate the skin. The lack of calcification and the history of trauma are helpful points to clarify the diagnosis; both lesions are often asymptomatic. The glomus tumor is a very painful, lucent defect affecting the distal phalanx by means of pressure erosion. An abnormal dilation of blood vessels in a tightly compartmentalized area like the distal phalanx creates the characteristic pressure destructive lesions.

In long bones it is important to be able to differentiate enchondroma with heavy calcification (calcifying enchondroma)11 from a medullary bone infarct. The pattern of calcification is often very helpful with the enchondroma providing so-called rings or broken rings, small, rounded calcification surrounded by a lucent matrix. In contrast, a bone infarct creates a streaky, roughened calcification with peripheral borders which have been called serpiginous in appearance. In addition, the infarct is often surrounded by a characteristic fibro-osseous margin, which may assume a well-defined straight line on one side of the lesion, a feature seldom observed in an enchondroma. The roentgen sign of bone expansion favors enchondroma, since a medullary bone infarct does not expand bone.

Malignant transformation of a solitary enchondroma to a chondrosarcoma is rare. It appears to occur in the bones closest to the axial skeleton. Malignant changes are more frequent in the long tubular bones than in the small bones of the hand and feet.12 Patients develop unrelenting pain in a lesion that was previously asymptomatic. The radiologic features that suggest malignant transformation are cortical disruption, focal malignant periosteal reaction, a poor zone of transition, and a large, soft tissue mass.

Treatment and Prognosis 

Most lesions in the hands or feet that create no cosmetic deformity require no treatment at all. Others that are in the long tubular bones or that create significant expansion in the small tubular bones require careful curettage followed by cryosurgery with bone chip packing.13 The closer the enchondroma is to the axial skeleton, the higher the potential for malignant degeneration; therefore, some surgeons will remove these lesions prophylactically when they are in this location. Irradiation of benign cartilaginous lesions is absolutely contraindicated.14

References

  1. Takigawa K. Chondroma of the bones of the hand—a review of 110 cases. J Bone Joint Surg (Am) 1971; 53:1591.
  2. Dahlin DC. Bone Tumors, 2nd ed. Springfield: Charles C. Thomas, 1967.
  3. Poznanski AK. The Hand in Radiologic Diagnosis. Philadelphia: W.B. Saunders, 1974.
  4. Levy WM, Aegerter EE, Kirkpatrick, Jr. JA. The nature of cartilaginous tumors. Radiol Clin North Am 1964; 2:237.
  5. Wilner D. Radiology of Bone Tumors and Allied Disorders. Philadelphia: W.B. Saunders, 1982.
  6. Edeiken J. Roentgen Diagnosis of Diseases of Bone, 3rd ed. Baltimore: Williams & Wilkins, 1981.
  7. Braddock GTF, Hadlow VD. Osteosarcoma in enchondromatosis (Ollier’s disease). Report of a case. J Bone Joint Surg (Br) 1966; 48:155.
  8. Lammot TR. Enchondroma of the patella. A case report. J Bone Joint Surg (Am) 1968; 14:1230.
  9. Potdar GG, Srikhande SS. Chondrogenic tumors of the jaws. Oral Surg 1970; 30:649.
  10. Bell MS. Benign cartilaginous tumors of the spine. Br J Surg 1971; 58:707.
  11. Laurence W, Franklin EL. Calcifying enchondroma of long bones. J Bone Joint Surg (Br) 1953; 35:224.
  12. Hamlin JA, Adler L, Greenbaum EI. Central enchondroma—A precursor to chondrosarcoma? J Can Assoc Radiol 1971; 22:206.
  13. Jewusiak EM, Spence KF, Sell KW. Solitary benign enchondroma of the long bones of the hand. Results of curettage and packing with freeze-dried cancellous bone allograft. J Bone Joint Surg (Am) 1971; 53:1587.
  14. Yochum TR, Rowe LJ. Essentials of Skeletal Radiology, 2nd ed. Baltimore: Williams & Wilkins, 1996.

About the Authors

Dr. Terry R. Yochum is a second generation Chiropractor and a cum laude graduate of the National College of Chiropractic, where he subsequently completed his radiology specialty. He is a Diplomate of the American Chiropractic Board of Radiology and served as its vice-president and president for seven years (1983-1990).

Dr. Michael S. Barry is a 1988 cum laude graduate of Palmer College of Chiropractic. He completed a three-year radiology residency at Logan College of Chiropractic following two years of clinical practice in Las Vegas, Nevada. He received his diplomate in radiology from the American Chiropractic Board of Radiology in 1992.

Dr. Chad J. Maola is a 1999 magna cum laude graduate of National College of Chiropractic.