Benign bone tumors

Reverse Carpal Tunnel Syndrome

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Primary bone tumors of the carpus are rare [14]. The two most common lesions, osteoid oste-oma and enchondroma, may be easily misdiag-nosed as IOG. Enchondromas may cause pathologic fractures, especially of the scaphoid, just as they do in the phalanges. The giant cell tumor, although more often originating from the distal radius instead of the carpus, routinely causes carpal destruction. Other benign bone tumors, including osteochondroma, chrondroblas-toma, chondromyxoid fibroma, hemangioma, aneurysmal bone cyst, and osteoblastoma, are described in case reports.

Intraosseous Ganglion Lunate Mri
Fig. 5. Imaging an intraosseous ganglion of the capitate. (A) CT clarifies the sclerotic cortical rim that surrounds an IOG. (B) MRI illustrates the homogenous internal architecture expected of a ganglion.
Intraosseous Ganglion Scaphoid

Fig. 6. Treatment of a scaphoid intraosseous ganglion. (A) Preoperative cross-sectional imaging precisely localizes the location of the lesion. (B) Intraoperative biplanar fluoroscopy facilitates precision curettage. (C) Graft is taken from the distal radius to reconstitute the bone of the proximal pole.

Fig. 6. Treatment of a scaphoid intraosseous ganglion. (A) Preoperative cross-sectional imaging precisely localizes the location of the lesion. (B) Intraoperative biplanar fluoroscopy facilitates precision curettage. (C) Graft is taken from the distal radius to reconstitute the bone of the proximal pole.

Osteoid osteoma

An osteoid osteoma is a benign osteoblastic tumor typically found in the long bones of persons between the ages of 10 and 30. It is composed of a central core of osteoid and bony trabeculae surrounded by highly vascular fibrous connective tissue. Grossly, the tumor is well-circumscribed, with a reddish-brown nidus.

Osteoid osteomas cause a constant focal pain at the site of the tumor. Pain is worse at night, and is dramatically relieved with small doses of aspirin or other salicylates. Although rare in the carpus, the osteoid osteoma must be considered in the differential diagnosis of wrist pain in adolescents or young adults [15,16]. The usual sign is point tenderness over the involved bone. A case of carpal tunnel syndrome has been attributed to an os-teoid osteoma causing the contour of the capitate to project volarly into carpal canal [17].

Osteoid osteomas may be found anywhere in the carpus, but most lesions have been reported in the scaphoid, hamate, and capitate [16,18,19]. Classically, radiographs show a discrete central nidus of bone surrounded by an area of lucency enclosed within a dense ring of sclerosis; a target-shaped lesion. Within the diminutive bones of the hand and wrist, the tumor may appear purely osteolytic, similar to an IOG. Other atypical radiographic features may also be present, including subtle changes in bone density and cortical irregularities or hypertrophy. Plain radiographs may even be normal [20]. A bone scan shows very high technetium Tc 99m diphosphonate uptake. CT reliably identifies the bony nidus at the core of the tumor [16]. Roent-genographically distinct multiple nidi have been reported in the scaphoid and capitate [21].

An osteoid osteoma is never an incidental finding; pain is universal. Nonetheless, the tumor may regress spontaneously, so a period of aspirin therapy may be considered. In the wrist, lesions are surgically accessible, so all reports in the literature involve operative management. Resection of the nidus is curative [19,20,22] and recurrence is rare [16,23]. The authors pack the defect with local cancellous bone graft, although removing the lesion is clearly the most important factor in pain relief [22]. A recent study [24] demonstrated successful treatment of osteoid osteomas of the upper extremity using radiofrequency ablation; however, this technique is not currently recommended for the carpal bones because of the proximity of neurovascular structures.

Enchondroma

A chondroma is a benign cartilaginous neoplasm of bone. Usually the tumor arises within the medullary cavity of a tubular bone and is known as an enchondroma. A chondroma may also originate on the surface of bone—a juxtacortical or periosteal chondroma. The tumor is composed of mineralized or unmineralized hyaline cartilage, and appears pearly gray on gross inspection.

The enchondroma is the most common primary bone tumor in the hand, and has a particular predilection for the proximal phalanges of young adults. Less frequently, enchondromas of the hand occur in the metacarpal, followed by the middle phalanx, and lastly the carpus [25]. Taki-gawa [26] reviewed 110 cases of chondromas in the hand, and only identified two in the carpus, one scaphoid and one lunate. Similarly, as a proportion of all carpal lesions, enchondromas are uncommon. Of 86 carpal bone lesions treated by Emecheta and colleagues [27], only three were enchondromas.

Most carpal enchondromas occur in the scaphoid, and most are usually minimally symptomatic until a pathologic fracture occurs [26-31]. Takka and Poyraz [31] reviewed eight cases of scaphoid enchondroma in the literature, five of which presented with a pathologic fracture. In their case, an 11-year-old boy had mild pain but no fracture. Periosteal chondromas may cause mechanical or compressive symptoms, including carpal tunnel syndrome [32]. Malignant change is very rare in solitary chondromas, and it has not been reported in the carpus.

Enchondromas replace normal medullary bone, creating radiographically well-defined margins. In the hand, enchondromas may be quite expansive, commonly causing endosteal scalloping and significant cortical thinning. Chondral calcification occurs throughout the lesion and appears as rings and arcs on plain radiograph; a "stippled" appearance. CT clarifies this punctate matrix mineralization, distinguishing this lesion from an intraosseous ganglion, osteoid osteoma, or other process. CT is also useful for assessing the integrity of the cortex and the configuration of pathologic fractures.

Carpal enchondromas are treated more aggressively than those in the proximal phalanx, owing to the frequency of the tumor in the scaphoid and the risk of a pathologic fracture. Most carpal cases are treated with curettage and grafting of the lesion with autograft from the distal radius or iliac crest. Corticocancellous graft may sometimes by necessary to restore the osseous architecture of the scaphoid [27]. If the vascularity of the scaphoid is compromised by extensive curettage, a vascular-ized 1,2 intracompartmental supraretinacular artery graft may be used [28]. Notably, the osteolysis, sclerosis, and dystrophic calcification associated with a cystic scaphoid nonunion may be difficult to differentiate from the architecture of a pathologic scaphoid fracture caused by an en-chondroma. The diagnosis is facilitated by MRI, which shows the nonmineralized portion of the enchondroma.

Giant cell tumor

A giant cell tumor (GCT) is a benign but locally aggressive tumor that should be considered in the differential diagnosis of any osteolytic bone lesion. The GCT is composed of multinucleated giant cells within a sea of homogenous stromal cells. Notably, giant cells may be present in other lesions found in the carpus, including aneurysmal bone cysts, chondroblastomas, chondromyxoid fibromas, the bone lesions of hyperparathyroid-ism, and giant cell-containing osteosarcomas.

GCTs are most common in skeletally mature young adults. The tumors generally present with slowly progressive pain, and sometimes a soft tissue mass. Radiographs demonstrate a well-defined radiolucency in the epiphyseal region of a long bone. The tumor obliterates the medullary cavity, and often expands through the adjacent cortex. The distal radius is the third most common site for GCTs and, not infrequently these lesions are aggressive enough to involve the nearby carpus.

GCTs may also arise primarily from a carpal bone. In a review of previously published series, Averill and colleagues [33] found 4 of 1200 GCTs originating in the carpus. Overall, 2% of GCTs occur in the bones of the hand, and 18% percent of GCTs in the hand are multicentric. Averill and colleagues [33] recommend a bone scan to look for additional foci when a GCT in the hand is identified. In their series of 28 GCTs of the hand, the authors report one case in the carpus—a multicen-tric tumor of the hamate and trapezoid [33].

Patients who have GCTs of the carpus complain of dorsal wrist swelling, pain, and limited motion. Symptoms may mimic other diseases such as basal joint arthritis [34]. Unlike the radiographic appearance of GCTs elsewhere, GCTs of the carpus typically manifest as a radiolucency without expansion of the bone [33-38]. Differentiation from other carpal lesions such as an intra-osseous ganglion is difficult. FitzPatrick and Bullough [38] reported a case of the lunate that ra-diographically appeared to be Kienbock's disease.

GCTs localized to a carpal bone are best treated by en bloc excision of the affected bone. Curettage alone has a 100% recurrence rate, and curettage with adjuvant (eg, liquid nitrogen) has not been proven more effective. Lane and colleagues [35] reported cases of GCTs in the lunate and capitate that recurred after curettage and grafting. Likewise, a GCT of the capitate recurred after curettage and grafting by Howard and

Lassen [36]. All three of these cases resolved after total or near total excision of the carpal bone. In cases treated primarily with excision of the affected bone, there have been no reported recurrences [37,38].

GCTs of the carpus have the potential to infiltrate the adjacent tissues, similar to GCTs of the distal radius. Weiner and Leeson [34] reported a case of a GCT of the trapezium that invaded into the trapezoid and thenar musculature. The authors have seen a very aggressive GCT destroy the entire proximal carpal row, and infiltrate vol-arly and dorsally into the adjacent soft tissues (Fig. 7). Wide excision of expansive tumors is necessary, because the most important factor governing the rate of local recurrence is the margin at the time of the surgical procedure. The entire carpus and some of the distal radius may need to be removed. Reconstruction may require wrist fusion, possibly using a free vascularized fibula graft as described in the literature for distal radius GCTs [39-43].

Other benign bone tumors

The carpal bones develop as expanding chon-dral centers of ossification, and can potentially be home to any musculoskeletal neoplasm that occurs in cartilage or bone. Chondroblastoma [44] and chondrommyxoid fibroma [45] are rare chondral lesions in the carpus. Osteoblastoma, the larger counterpart of the osteoid osteoma, is an uncommon bone producing carpal tumor [46,47]. The osteochondroma also may originate in the carpus and cause tendon irritation and other mechanical symptoms [48,49]. Finally,

Giant Cell Osteoid Osteoma

Fig. 7. Giant cell tumor of the wrist. (A) Lateral radiograph shows the expansive osteolytic appearance characteristic of GCTs about the wrist. (B) MRI demonstrates infiltration of the tumor into the adjacent soft tissues. (C) Bivalved specimen reveals preservation of the distal radius and obliteration of the carpus, suggesting a carpal origin for the tumor.

Fig. 7. Giant cell tumor of the wrist. (A) Lateral radiograph shows the expansive osteolytic appearance characteristic of GCTs about the wrist. (B) MRI demonstrates infiltration of the tumor into the adjacent soft tissues. (C) Bivalved specimen reveals preservation of the distal radius and obliteration of the carpus, suggesting a carpal origin for the tumor.

benign bone tumors may contain an aneurysmal bone cyst (ABC), or an ABC may arise de novo in the carpus [50,51]. In each case, curettage and grafting is an acceptable preliminary surgical treatment, because the diagnosis is often not made until pathologic examination.

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