HISTORY AND PHYSICAL EXAMINATION
A 42-year-old woman presented with pain on the lateral aspect of the right elbow, associated with a slowly enlarging mass for the previous 6 months. Eight years before presentation, she had a resection of a benign chondroid tumor from the distal humerus after which she did not receive any adjuvant therapy. Two years before presentation, she returned to the original surgeon for evaluation of lateral elbow pain at the surgical site. A repeat radiograph was obtained, which was interpreted as without change from prior films, and no additional treatment was recommended. She denied any constitutional symptoms such as fever, chills, or weight loss.
Physical examination of the right elbow revealed a well-healed surgical scar overlying a discrete 2 × 3 cm mass just proximal to the lateral epicondyle, which was tender to palpation. There were no skin changes or axillary lymphadenopathy. Muscle testing revealed full strength of all groups except for some weakness of right ring finger extension, graded 4 out of 5. An EMG-NCV study indicated mild compression at the radial tunnel.
Preoperative plain radiographs of the right elbow before the initial excision were not available. Imaging studies available for evaluation include immediate postoperative radiographs of the right elbow after initial resection (Fig 1A), repeat radiographs 6 years after resection (Fig 1B), current radiographs (Fig 1C), and current MRI with gadolinium (Fig 2). Based on the history, physical examination, and imaging studies, what is the differential diagnosis?
The immediate postoperative radiograph (Fig 1A) shows postsurgical irregularity of the distal lateral humeral cortex. On radiographs taken 6 years later, development of a cortically based lytic expansile lesion is seen (Fig 1B), which increased in size over 2 years (Fig 1C). The lesion is well-defined medially and elevates the periosteum superiorly. A thin layer of peripheral calcification is seen laterally, possibly representing a thin layer of periosteal new bone formation. No aggressive periosteal new bone formation is seen.
A magnetic resonance imaging (MRI) scan done at the time of presentation shows a 1.5 cm lesion isointense to skeletal muscle on T1-weighted images (Fig 2A) with diffuse enhancement after contrast administration (Fig 2B). On T2-weighted images the lesion is hyperintense to skeletal muscle but hypointense to joint fluid with slight heterogeneity (Fig 2C). Inversion recovery images show very high signal intensity, isointense to the joint fluid (Fig 2D).
Aneurysmal bone cyst
Intra/juxtacortical chondromyxoid fibroma
The patient was taken to the operating room for an excisional biopsy and aggressive curettage. At the time of surgery, the lesion was noted to be completely intracortical and juxtacortical with no extension into the medullary canal (Figs 3, 4). Based on the history, physical findings, laboratory tests, radiographic studies, and histologic picture, what is the diagnosis, and how should this lesion be treated?
Histologic examination of the tissue showed lobules of spindled to stellate-shaped cells in an abundant myxoid to chondroid stroma and intermixed fibrous septae (Fig 3). Islands of chondroid material containing oval to stellate- shaped cells were surrounded by a hypercellular population of cells resembling chondroblasts and fibroblasts and prominent vessels (Fig 4). No significant atypia was present and mitotic figures were not identified.
Intracortical chondromyxoid fibroma
DISCUSSION AND TREATMENT
Chondromyxoid fibroma is the least common of benign bone tumors of chondroid origin. It was first described by Jaffe and Lichtenstein in 19488 and identified as a distinct entity with a benign clinical course. Patients typically present in the second and third decade, but individual cases have been reported from first to eighth decades. There is a slight male predominance of the tumor. The most common presenting symptom is transient pain, rarely with a palpable mass, of months or years duration. These lesions infrequently are discovered incidentally.
Magnetic resonance imaging (MRI) can help in establishing the diagnosis. Radiographic appearances of periosteal chondromas consist of scalloping or remodeling of the adjacent cortex because of pressure, presence of a cartilage matrix, and occasionally a soft tissue mass.19 Osteoblastomas have variable radiographic appearance but usually manifest as an expansile lytic lesion with varying amounts of osteoid production. Aneurysmal bone cysts frequently show septations and fluid-fluid levels on MRI because of bleeding into the cystic cavities.12 Intracortical abscesses would show inflammatory changes in the overlying soft tissues. Intracortical hemangiomas are rare and typically show internal, vertically oriented calcified trabeculae, as seen in the intramedullary and vertebral locations.13 Nonossifying fibromas are frequently hypointense and septated on T2-weighted images because of hypercellular fibrous tissue and hemosiderin deposition, although some are hyperintense on T2-weighted images and also are enhanced, as seen in this case.9
Chondromyxoid fibroma usually occurs eccentrically in the metaphysis of long bones, mostly in the lower extremities, with the most common site (45%) being the proximal tibia. Approximately 25% of cases occur in the collective bones of the feet and flat bones, such as the ilium and ribs.
The humerus, as in this case, is involved in only 5.4% of cases.23 Extension into the diaphysis or epiphysis is uncommon, with the latter more common than the former.23 In the English literature, intracortical location has been reported four times,5,21 juxtacortical location 14 times,1,4,14,16,21 and one case of apophyseal location.15 Interestingly, two of the four previously reported intracortical chondromyxoid fibromas were in the humerus, as in this case.
Grossly, the tumor is typically sharply circumscribed, firm, lobulated, and tan-white to blue-gray. Histologically, chondromyxoid fibroma is characterized by myxoid, chondroid, and cartilaginous elements, as its name implies, with a lobulated architecture. Tumor lobules are composed of spindled to stellate shaped cells with a rich eosinophilic cytoplasm in a chondromyxoid stroma. Microscopic calcification is uncommon and can occur in 6.8%4 to 34.1%24 of cases. Areas at the periphery of lobules show more cellularity. The fibrous component accounts for a smaller portion of the tumor, found in thin septa between the nodules. These septa contain vasculature, multinucleated giant cells, and occasionally osteoid. About 1/3 of tumors have atypical cells with large, often bizarre nuclei, superficially reminiscent of a chondrosarcoma. Mitotic figures usually are absent, and only a small number of tumors have foci of necrosis. Caution should be exercised in differentiating this tumor from chondroblastoma or chondrosarcoma, especially on fine-needle aspirates.11 Genetically, it has been suggested that there are several distinct break points on the long arm of chromosome 6 that may be involved nonrandomly in chondromyxoid fibromas.20 Another report isolated an unbalanced translocation between chromosomes 3 and 6 in the regions involving the Type X collagen gene and the parathyroid hormone-related peptide receptor gene (PTH-PTHrP), which functions to control growth and maturation of endochondral bone.6 Chromosomes 2, 5, and 13 also have been implicated in pathogenesis of chondromyxoid fibroma.2,22
Radiographically, the typical appearance of chondromyxoid fibroma is of an eccentric metaphyseal lytic lesion with sharp, usually scalloped and sclerotic margins. Radiographic features are most helpful in distinguishing chondromyxoid fibroma from other cartilage lesions because of morphologic overlap. Expansion of the tumor can cause erosion of the overlying cortex. Cortical breakthrough, periosteal reaction, and soft tissue extension are uncommon. Matrix mineralization is present in only 7.5% of cases, with older patients and flat bone location more commonly exhibiting this feature.24
On MRI, chondromyxoid fibroma appears heterogeneous because of the chondroid, myxoid, and fibrous tissues that comprise it. On T1 imaging the lesion is isoin- tense to muscle, and on T2 imaging it shows high heterogeneous signal intensity. After administration of gadolinium, the lesion typically enhances heterogeneously.
The prognosis of chondromyxoid fibroma is excellent, even in recurrent cases. Previously, en bloc resection with tumor free margins had been the treatment of choice, considering curettage with grafting results in a 12.5% to 40% recurrence rate.17,18 More recently, it has been accepted that the treatment of choice in nonexpendable bones is extended intralesional curettage with creation of a cortical window large enough to observe the entire lesion, aggressive curettage, and use of a burr and pulsatile lavage with or without adjuvants like phenol.3 Recurrence has been reported up to 30 years postresection,10 and has been reported to occur in the soft tissues around the site of surgical extirpations.7
The potential differential diagnoses of intracortical lesions can range from benign (eg, chondromyxoid fibroma) to malignant (eg, osteosarcoma). Additional factors, such as similarity of histology between benign and malignant entities (eg, chondromyxoid fibroma and chondrosarcoma), and occasional lack of typical diagnostic features of chondromyxoid fibroma may complicate the picture. For these reasons, we recommend that musculoskeletal lesions, especially intracortical lesions, be confirmed and treated by musculoskeletal oncology centers.
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