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Hereditary multiple exostoses with malignant transformation

Case contributed by Matt Skalski
Diagnosis certain


Pelvic pain, difficulty with urination and defecation

Patient Data

Age: 35 years
Gender: Male

There is a large mass within the pelvic outlet which demonstrates a fine ring and arc pattern of calcification. The mass occupies the majority of the diameter of the pelvic basin. 

On the pelvic outlet projection, the mass appears to arise from the posterior aspect of the right pubic ramus as the cortex is indistinct in this region, although this site of origin is unclear in the current study. 

Note that there are multiple sessile osseous excrescences along the proximal right femur including the proximal right femoral neck (Brahman bull appearance) and metaphysis, as well as pedunculated excrescences at the lesser trochanter and femoral neck on the left, and anterolateral ilium on the right. These excrescences demonstrate medullary continuity with their parent site.

The lungs show no evidence of metastatic involvement. Note the multiple sessile osteochondromas along the proximal right humerus, as well as one partially visible sessile osteochondroma on the left humerus. Other osteochondromas are noted at the right clavicle and right scapula. 

The mass lesion is again identified within the pelvis, and appears to originate from an osteochondroma at the posterior aspect of the right superior pubic ramus. The mass lesion measures 15 x 9.4 x 14 cm in AP, transverse, and superoinferior dimensions, respectively. The mass demonstrates a rings-and-arc pattern of calcification, suggesting a chondroid matrix.

The mass displaces the urinary bladder, which is decompressed with an indwelling Foley catheter. The mass also has a mass effect on the rectum, displacing it posteriorly and to the left.

The mass lesion does not demonstrate any vessel or neurovascular bundle encasement. No additional mass lesions are identified.

Case Discussion

Malignant degeneration of an osteochondroma in patients with hereditary multiple exostoses is the most feared complication of the disease. When osteochondromas become malignant, the cartilaginous cap is the part that transforms most often into chondrosarcoma, as is the case in this patient. This patient also reported that he had multiple family members with bony bumps, illustrating the autosomal dominant inheritance pattern of the disease.

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