Radiation-Induced Focal Cortical Necrosis of the Femur after Sarcoma Treatment Presents As Lytic Lesions (Slideshow)

By Hakan Ilaslan, MD; Jean Schils, MD; Michael Joyce, MD; Chirag Shah, MD; and Yaxia Zhang, MD

Soft tissue sarcomas often require radiation prior to and after limb-sparing surgery. Post-treatment radiation-induced necrosis is a well-known and potentially severe dose-related complication that usually involves medullary bone. Cortical bone, on the other hand, is considered one of the most radioresistant structures of the body.

This slideshow features two unusual cases from Cleveland Clinic’s Sarcoma Program/Musculoskeletal Tumor Center. These patients developed radiation-induced necrosis of cortical bone after treatment with neoadjuvant radiation (66 Gy) and surgical resection for soft tissue sarcoma in the thigh. Biopsy of their lesions confirmed isolated circumscribed intracortical necrosis attributed to radiation.

To our knowledge, these are the first reported cases of isolated radiation necrosis of cortical bone.

Takeaway for orthopaedic surgeons

When bone metastases or recurrent tumor occur after sarcoma treatment, the appearance is typically very aggressive with lytic-destructive behavior, and soft tissue extension is common. Radiation-induced sarcoma may present as a lytic lesion, though it usually appears as very aggressive with cortical destruction and a soft tissue mass. It develops with a median latency period of 12 years after the conclusion of radiation treatment. In the setting of previous high-dose radiation, a well-defined lytic lesion limited to the cortical bone without periostitis may be an early manifestation of radiation necrosis.

Full discussion of these cases can be found in Skeletal Radiology, where they were first reported.

<p>A 32-year-old female presented with a one-month history of a slightly tender mass involving the right distal leg laterally. Coronal T2-weighted magnetic resonance (MR) image of the right thigh showed a heterogeneous soft tissue mass within the vastus lateralis muscle (arrows). An image-guided biopsy of the mass revealed histology consistent with myxoid liposarcoma.</p>

<p>Staging radiologic studies did not reveal a distant metastasis. Radiation oncology treated the patient with a total of 50 Gy of radiation over five weeks before surgery, with the radiation port covering the tumor and adjacent femoral cortex. The tumor responded with a significant decrease in size. An orthopaedic oncologist performed a radical resection of the mass. After surgery, 16 Gy of boost radiation was administered at the superolateral aspect of the surgical bed, a radiation field that included the adjacent femoral cortex. Pre- (a) and postoperative (b) radiation planning CT images demonstrated the coverage window of soft tissues and adjacent femoral cortex.</p>

<p>Follow-up radiographic imaging at three and 16 months after treatment were normal. However, radiographic follow-up at 19 months (above) showed a new, well-defined, elongated, approximately 2 cm lytic lesion in the lateral cortex of the distal femur underlying the surgical bed (arrows). AP (a) and lateral (b) radiographs of the right femur.</p>

<p>CT-guided biopsy of the lesion with an 11-gauge biopsy needle.</p>

<p>MRI performed one month later confirmed the presence of an intracortical lesion without cortical destruction or periostitis. There was no recurrent or residual sarcoma in the soft tissues of the surgical bed. Coronal (a) and axial (b) T2-weighted fat-suppressed MR images of the right femur showed an intracortical lesion with hyperintense signal (arrows). Axial T1-weighted precontrast image (c) showed slightly hyperintense signal of the lesion compared to adjacent skeletal muscle (arrows). Postcontrast T1-weighted fat-saturated axial image demonstrated predominantly peripheral enhancement of the lesion (d).</p>

<p>Our multidisciplinary Sarcoma Tumor Board recommended biopsy of the lesion under computed tomography (CT) guidance. The biopsy revealed histology consistent with nonspecific necrosis, attributed to radiation treatment. High-power view (400×) of a lytic lesion near the periphery of the biopsy specimen shows necrotic bone trabeculae, bone dust and fatty necrosis. Note that the osteocyte lacunae in the bone are empty (arrows) and there are fat vacuoles (curved arrows) in the area of fat necrosis. She was followed with serial radiographic and MR imaging, which demonstrated the stability of the lesion over 18 months. However, because she complained of intermittent discomfort in the region of the distal femur, so prophylactic surgical rodding of the femur was performed to prevent a fracture caused by underlying radiation osteitis. The patient has been asymptomatic and remains free of metastatic disease five years after the surgery.</p>

<p>A 69-year-old female presented to a general orthopaedic surgeon at an outside institution with a gradually enlarging upper left thigh mass for over five months. Surgical resection of the mass was performed without preoperative imaging or biopsy. Histology showed undifferentiated pleomorphic sarcoma. The patient was referred to our institution for evaluation by an orthopaedic oncologist. Gross pathology of the specimen showed negative margins. All staging radiologic studies, including chest CT, were negative. After discussing the case at our Sarcoma Tumor Board, a decision was made to administer radiation treatment and follow-up by serial MRIs. A total radiation of 66 Gy was given over four months. The radiation field included soft tissues at and around the surgical bed and adjacent femoral cortex. Axial (a) and coronal (b) radiation planning CT images demonstrated coverage window of soft tissues and adjacent femoral cortex. Follow-up imaging radiographs and MRI remained normal for two years.</p>

<p>An AP radiograph of the left femur demonstrates surgical clips and mild cortical thickening 19 months after the completion of radiation treatment.</p>

<p>However, a follow-up radiograph at 31 months after treatment shows a new well-defined, ovoid lytic lesion of the lateral cortex (arrow). </p>

<p>At 31 months post-treatment, coronal STIR (a), axial T2-weighted fat-suppressed (b) and T1-weighted (c) MR images of the right femur showed an intracortical lesion with hyperintense signal (arrow). Post-contrast T1-weighted fat-saturated axial image (d) demonstrated nodular, peripheral enhancement of the lesion superficially (arrow). Total body bone scan after MRI showed no abnormal uptake. A CT-guided biopsy showed blood and acellular fibrin debris without malignant cells, suggestive of necrosis. Prophylactic femoral rodding was not considered given the patient’s lack of symptoms. She remains asymptomatic over three years after the completion of her treatment.</p>

Slide 1/10

Dr. Ilaslan is a musculoskeletal radiologist who specializes in bone and soft tissue tumors, and tumor ablations. Dr. Schils is a musculoskeletal radiologist. Dr. Joyce is Co-Director, Musculoskeletal Tumor Center. Dr. Shah is Director of Clinical Research, Department of Radiation Oncology, and Dr. Zhang is a pathologist specializing in bone tumors now at Hospital for Special Surgery.