Neoplastic and tumorlike lesions detected on MR imaging of the knee in patients with suspected internal derangement: Part I, intraosseous entities

Thin Cartilage Cap May Be Related to the Spontaneous Regression in Pediatric Patients with Osteochondroma

BACKGROUND

The spontaneous regression of osteochondromas is rare, and only a few cases have been reported. Furthermore, the precise mechanism underlying spontaneous regression is unknown. This study aimed to examine the radiological findings of osteochondromas that had spontaneous regression and to identify potential indicators of this uncommon phenomenon in skeletally immature patients with osteochondromas.

METHODS

We included 28 patients (15 males and 13 females) who met the eligibility criteria between 2002 and 2019. The mean age at initial diagnosis was 9.7 years old (2-16 years). The mean follow-up period was 6.4 years (3-16 years).

RESULTS

Of the 28 patients, 10 (35.7%) had osteochondroma resolution. The osteochondroma resolved in one patient and regressed in nine. Tumor shrinkage is related to the thickness of the cartilage cap. The thickness of the cartilage cap did not correlate with age.

CONCLUSIONS

Tumor shrinkage is associated with a thinner cartilage cap on magnetic resonance imaging. The thickness of the cartilage cap may be an important predictor of spontaneous regression in pediatric patients with osteochondroma.

Osteochondromas: An Updated Review of Epidemiology, Pathogenesis, Clinical Presentation, Radiological Features and Treatment Options

Osteochondroma, the most common benign bone tumor, is a projection on the external surface of the bone, which can be sessile or pedunculated. 85% of osteochondromas present as solitary lesions, while 15% occur in the context of hereditary multiple exostoses (HME), a genetic disorder that is inherited in an autosomal dominant manner. Although often asymptomatic, symptoms may eventuate from compression of adjacent vessels or nerves, fractures, osseous deformities, bursa formation, or malignant transformation. Cartilage cap thickness >2 cm in adults or >3 cm in children as well as new onset of pain or growth, or rapid growth of the lesion, especially after the closure of the growth plate, might reflect cancerous transformation. Surgical resection is indicated for symptomatic lesions, complications, cosmetic reasons or malignant transformation. Excision of the tumor with free margin is the treatment of choice. Local recurrence is less than 2% if complete resection is achieved.

Dilemmas in distinguishing between tumor and the posttraumatic lesion with surgical or pathologic correlation

This article discusses the most common diagnostic dilemmas when trying to distinguish between tumor and sports injury or other trauma. Bone tumors frequently occur in the same young active patients who experience sports injuries. If the pain persists longer than expected, imaging studies should be obtained to prevent a delay in diagnosis or an inappropriate arthroscopy. A history of spontaneous fracture or a fracture after minor trauma should raise suspicion for underlying lesion as the cause. Occasionally necrosis and/or hemorrhage within a soft tissue sarcoma is so extensive that only a small cuff of viable tumor tissue is present.

MR imaging of primary bone tumors and tumor-like conditions in children

This article provides a review of the MR imaging features of the major primary malignant and benign bone tumors and tumorlike conditions encountered in the pediatric population. Malignant tumors discussed include osteosarcoma, Ewing sarcoma, chondrosarcoma, lymphoma, and malignant fibrous histiocytoma. Benign lesions discussed include simple bone cysts, aneurysmal bone cysts, giant cell tumor, osteochondroma, enchondroma, chondroblastoma, osteoid osteoma, osteoblastoma, nonossifying fibroma, fibrous dysplasia, osteofibrous dysplasia, hemangioma, and histiocytosis. The use of MR imaging in the diagnosis of these lesions is discussed, and the text is enhanced with imaging examples of the lesions.

MR imaging of the knee: incidental osseous lesions

The knee joint remains the articulation most frequently assessed by MR imaging, and osseous tumor and tumor-like lesions are not uncommon incidental imaging findings. This article reviews the most commonly encountered incidental lesions, emphasizing the characteristic MR imaging features. It is intended not as a complete review of the imaging findings associated with these lesions but as a summary, highlighting the MR imaging features that are most useful in suggesting a specific diagnosis. The authors organize incidental lesions into the following broad categories: cartilaginous, fibro-osseous, and degenerative. They do not address those lesions that are typically symptomatic and, as a result, likely to be directly related to the patients' clinical presentation and subsequent imaging.

Errors in the MRI evaluation of musculoskeletal tumors and tumorlike lesions

Interpretation of an MRI of a suspected musculoskeletal neoplasm can be extremely difficult. Fifty-six MRIs originally evaluated by outside radiologists were independently evaluated by an expert panel consisting of three specialized musculoskeletal radiologists. The outside reports were then graded based upon accuracy and completeness of the differential diagnosis. We compared the expert opinions with those of the outside radiologists. According to the expert panel, only 30 of the 56 (54%) outside reports listed the most likely diagnosis as such and only 35 (63%) listed it at all. A complete appropriate differential diagnosis was listed in only 22 (39%) of the outside reports. Furthermore, 18 (32%) of the outside reports listed diagnoses judged to be extremely unlikely by the experts. In a subset of 15 patients with images that the expert panel had judged diagnostic of specific entities, only nine of the outside reports listed the correct diagnosis as such and only 10 listed it at all. Furthermore, 11 (73%) of the outside reports listed extremely unlikely possibilities for these diagnostic images. We found a substantial difference between the expert and the outside opinions.

Haemangiomas around the knee mimicking medial meniscal tears. Report of two cases and review of the literature

There are few reports in the English literature of extra-articular lesions simulating intra-articular pathology of the knee. Two cases of histologically confirmed haemangiomas related to the distal femur, presenting with knee pain suggestive of medial meniscal damage, are reported. A 27-year-old woman presented with persistent anteromedial right knee pain despite having undergone two arthroscopies for medial meniscal damage. An MRI showed a soft tissue mass on the medial side of the distal femoral metaphysis. The symptoms resolved only after open resection of the lesion. Histology showed a periosteal haemangioma. The second patient, a 24-year-old woman, complained of posteromedial left knee pain for 3 months. Although a medial meniscal tear was suspected, an MRI showed a soft tissue mass close to the bone of the distal femoral diaphysis. The symptoms resolved after open resection of the lesion. Histology showed a soft tissue haemangioma. Both patients were asymptomatic with normal MRI scans 6 to 12 months postoperatively. Although meniscal tears can present in young patients without a history of trauma, an MRI is extremely useful in diagnosing other lesions causing similar symptoms. Haemangiomas around the knee are rare, in particular periosteal haemangiomas of the distal femur as no report has been found in the English literature.

Radiologic case study. Benign intraosseous lipoma

Intraosseous lipomas are uncommon lesions of bone most often diagnosed incidentally. They typically manifest a classic radiographic appearance, but CT or MRI may be useful in diagnosing lesions that are atypical or incompletely defined radiographically and avoid an unnecessary biopsy.