Imaging review of skeletal tumors of the pelvis--part I: benign tumors of the pelvis

Abstract

The osseous pelvis is a well-recognized site of origin of numerous primary and secondary musculoskeletal tumors. The radiologic evaluation of a pelvic lesion often begins with the plain film and proceeds to computed tomography (CT), or magnetic resonance imaging (MRI) and possibly biopsy. Each of these modalities, with inherent advantages and disadvantages, has a role in the workup of pelvic osseous masses. Clinical history and imaging characteristics can significantly narrow the broad differential diagnosis for osseous pelvic lesions. The purpose of this review is to familiarize the radiologist with the presentation and appearance of some of the common benign neoplasms of the osseous pelvis and share our experience and approach in diagnosing these lesions.

Figure 1

Middle-aged female presents with chronic pelvic pain. Frontal radiograph (a) of the abdomen reveals subtle cortical disruption and periosteal reaction involving the superior aspect of the right iliac crest (arrow). Subsequent CT examination (b) demonstrates a lytic destructive lesion of the right iliac bone, with a large soft tissue mass (asterisk).

Figure 2

31-year-old male presents with palpable hard mass lateral to right iliac crest diagnosed as an osteochondroma. Pelvic plain film (a) demonstrates an irregularly calcified, pedunculated lesion (asterisk) arising from the right iliac crest. It presents as a peripheral outgrowth with its cortex in continuity with the iliac bone (arrowheads). Axial T1 (b) and axial T2 fat sat. (c) MRI images of same lesion (asterisk) demonstrate the continuity of the cortex and medullary portion of the lesion with the parent bone (arrow) and identify a thin cartilage cap (arrowheads).

Figure 3

50-year-old male with osteoblastoma (aka giant osteoid osteoma) involving the left iliac bone. Plain radiograph (a) shows a large lytic left iliac bone lesion (asterisk) with sharp sclerotic borders. An angiographic image (b) with a 5 French cobra catheter (curved arrow) in the left common iliac artery demonstrates the vascular nature of the tumor, with the tumor blush (asterisk) predominantly supplied by the superior gluteal artery which was subsequently embolised a day prior to surgical resection. The axial CT (c) and axial T2 MRI (d) demonstrates the mass originating from the outer cortex of the right iliac bone. It has a narrow zone of transition with distinct borders. Edema is noted in the iliac bone (B) and the gluteal musculature (M) on the fluid sensitive T2 MRI sequence demonstrating the aggressive nature of this benign lesion. Axial T2 MRI (e) 5 years postresection demonstrates unusual progression to high grade osteoblastic osteosarcoma (arrows). Even though benign, osteoblastomas can be locally aggressive, recur or differentiate to a malignant aggressive tumor, in this case necessitating a revision hemipelvectomy.

Figure 4

40-year-old male with a large left iliac wing expansile mass diagnosed as pelvic giant cell tumor. Plain film (a) shows a large, lytic, destructive lesion in the right iliac wing with indistinct margins and cortical breakthrough (arrows), with no visible matrix. Left internal iliac artery angiogram (b) demonstrating the highly vascular nature of the tumor. Selective embolization of the superior gluteal artery (c) demonstrating embolization coils (arrowheads), and decreased tumor vascularity. Axial T2 fat sat MRI (d) and axial post-contrast CT images (e) demonstrating expansile nature of the giant cell tumor with multiple foci of necrosis (asterisk) and intervening tumor stroma. Size of the mass increased following embolization due to internal bleeding and necrosis. Displacement of surrounding soft tissues (Iliopsoas (P), gluteal musculature (G)), rather than invasion is illustrated. Note residual outer rim of expansile cortical bone (arrows), better appreciated on the CT scan.

Figure 5

61-year-old female with Mazabraud syndrome (polyostotic fibrous dysplasia and soft tissue myxomas (M)). Plain film (a) demonstrates multiple lucent lesions with ground glass matrix in the pelvis (asterisk) and long predominantly sclerotic abnormality in bilateral femurs (circle). Fibrous dysplasia is often described as a long lesion in the long bone. Coronal T1 (b) and STIR (c) MRI images demonstrating multiple fibrous dysplasia (F) lesions. Note that some of these maintain low to intermediate signal intensity on both T1 and T2 images (asterisk). Axial CT (d) and axial T2 fat sat (e) MRI images demonstrating contour abnormality of the left ilium with ground glass matrix and focal bone expansion (F). Multiple T2 bright myxomas (M) are noted in the gluteal musculature.

Figure 6

8-year-old male presented with left hip pain, diagnosed as Aneurysmal bone cyst. Plain film (a) demonstrates large expansile lytic lesion (arrows) involving medial left acetabulum extending to the inferior pubic rami (G: gonadal shield). Axial CT scan (b) obtained immediately following curettage and packing with bone allograft showing relatively dense material (asterisk) within the expanded left Ischium. Follow-up plain film (c) five years postsurgical curettage and embolization (note the embolization coils along the medial aspect of the hip) shows healing of the ABS with return to normal contour and course trabeculation. Unfortunately, a focus of recurrence is also noted in the superior acetabulum (asterisk). Local recurrence is not common, but possible.

Figure 7

Forty-six-year-old female with a lytic lesion in the left medial acetabulum, diagnosed as chondroblastoma. Plain film (a) and axial CT (b) demonstrating a lytic lesion with heterogeneous chondroid matrix and sharp scalloped margins. The tumor showed increased uptake on bone scan (c) (B: bladder). Plain film (d) demonstrating healed chondroblastoma following surgical curettage and cement packing.

Figure 8

Typical ages for benign and malignant osseous pelvic tumors.