History
52-year-old female who has a history of sarcoma in the right thigh. The patient is being seen for staging.
Findings
There is a bulky mass displaying hypermetabolism with central necrosis (Figures 21.1.1, 21.1.2, and 21.1.2A) seen in the right mid posterior thigh compatible with known malig- nancy. Multiple sites of photopenia are noted in the liver (Figures 21.1.3 and 21.1.3A) involving the left and right lobes consistent with hepatic cysts seen on CT. No abnor- mal uptake is seen in the chest. There is a focus of activity in the sigmoid colon (Figure 21.1.4) suspicious for a polyp or tumor; recommend flexible sigmoidoscopy.
Impression
1. Hypermetabolism in the right mid posterior thigh compatible with history of sarcoma, without evidence of metastatic disease.
2. Abnormal activity in the sigmoid colon; advise endoscopy.
Pearls and Pitfalls
• Total whole body PET-CT is helpful in detecting distant metastases. High-grade sarcomas are generally more FDG-avid than a low-grade lesions.2,5,8
Discussion
The histopathology of this mass in this patient was proven later to be a liposarcoma.
Liposarcoma is a malignant tumor that can occur anywhere fat is present. This tumor most typically presents between 40 and 60 years of age. Histologic subtype is a signif- icant prognostic indicator. Myxoid liposarcoma is often classified as an intermediate- grade tumor with a large metastatic potential. The treatment of choice is resection with a wide surgical margin. Liposarcoma is radioresponsive. Adjuvant radiation therapy can be given, either preoperatively or postoperatively, depending on the margin status.
21 Muscular Skeletal Tumors
Lalitha Ramanna and Sherief Gamie
Case 21.1
220
FIGURE21.1.2.
FIGURE21.1.2A.
FIGURE21.1.3. FIGURE21.1.3A.
FIGURE21.1.4.
Certain variants of liposarcoma have shown a higher incidence of regional nodal and extrapulmonary metastases. Regional adenopathy is generally well depicted with PET.
History
80-year-old female with a history of recurrent leiomyosarcoma. The current exam is being done to evaluate extent of disease.
Findings
There is a large pelvic mass (Figure 21.2.1) corresponding to the 8 cm ¥ 8.3cm low pelvic mass demonstrated on recent CT (Figure 21.2.2). This is seen to be between an anastomotic bowel staple line and the urinary bladder, superior to and compressing the urinary bladder. The mass is moderately and heterogeneously hypermetabolic with greater hypermetabolism at its periphery than at its center. There are three small nodular densities extending from or adjacent to the mass. Any one of these could be a separate mesenteric mass. All of these peripheral lobulations or adjacent nodular densities are intensely hypermetabolic. There is physiologic bowel activity. No abnor- mal focus is seen above the central midpelvic mass. Sigmoid diverticular disease and low-density liver lesions are noted. No abnormal hepatic activity is evident, consistent
Case 21.2
FIGURE21.2.1.
with cysts. The subcarinal soft tissue noted on CT is negative by 18-FDG PET scintig- raphy. Incidental findings include sigmoid diverticulosis and atherosclerotic vascular disease. Multilevel degenerative disease in the lumbar spine is noted.
Impression
There is a large central pelvic mass above and compressing the urinary bladder and just below an anastomotic staple line. This is heterogeneous in activity with moderate activity centrally and multifocal sites of peripheral intense hypermetabolism. Several lobulations or adjacent nodular densities are intensely hypermetabolic. No distant disease is evident.
Pearls and Pitfalls
• Heterogeneous uptake of FDG is typical for pelvic leiomyosarcoma.2,5,8
Discussion
Leiomyosarcoma is a subgroup of sarcoma and is more commonly seen in gynecologic malignancies. The mean patient age at diagnosis is about 60 years old. Leiomyosar- coma frequently is diagnosed after a hysterectomy is performed for a presumed leiomyomatous uterus. Pure leiomyosarcomas constitute about 20% to 50% of uterine sarcomas. Leiomyosarcomas are relatively radio-insensitive to treatment. Chemo- therapy has limited success rate. Cisplatin has a total response rate of only a 3% with leiomyosarcomas. Newer agents, such as Ifosfamide, have been used in phase II trials for advanced or recurrent tumor, with a response rate of 17%.
224 Part II Clinical Cases
FIGURE21.2.2.
The 5-year survival rate for leiomyosarcomas can range from 17% to 65% based on mitotic rate. The recurrence rate is 71%.
History
19-year-old male who has a history of a left ankle mass. A biopsy was positive for osteosarcoma. His MR demonstrated a left calcaneus mass measuring 3.2 cm. An outside CT chest was unremarkable. The patient is being seen for staging.
Findings
There is a large and well-demarcated hypermetabolic mass (Figure 21.3A.1) seen involving the medial and lateral aspect of the left calcaneus (Figures 21.3A.2 and 21.3A.3) and tarsal bone (Figure 21.3A.4) with corresponding soft tissue mass and bony destruction on CT. There is mild soft tissue uptake involving right lateral foot com- patible with pressure from altered weight bearing. The mild activity in the thymus (Figure 21.3A.5) is considered normal for age. CT of the chest demonstrates no evi- dence of metastatic disease.
Impression
Hypermetabolism involving the left calcaneus and tarsal bone consistent with malig- nancy, without evidence of regional or distant metastases.
Pearls and Pitfalls
• Low-grade osteosarcomas can produce false-negative results on PET because FDG uptake tends to be low.2,5,8
• PET has the ability to identify recurrent tumor earlier than conventional imaging.9
• FDG imaging can accurately depict histopathologic response to therapy.1,4,6
• The sensitivity for soft tissue tumors is 87% and specificity 79%. The positive predic- tive value for high-grade tumors is higher than that for lower-grade tumors.2,5,8
Case 21.3A
FIGURE21.3A.1.
FIGURE21.3A.2.
FIGURE21.3A.3.
FIGURE21.3A.4.
FIGURE21.3A.5.
Discussion
Osteogenic sarcoma is a rapidly proliferating tumor and usually presents as a primary malignant bone tumor. It is the most common bone tumor encountered in the first three decades of life and has an incidence rate of 2.6% of all childhood cancers. It is more common in males. The peak incidence is at 13 to 14 years of age. The incidence of osteogenic sarcoma is increased in patients with Paget’s disease and bones that have previously been irradiated. This is why there is a second prevalence peak in older indi- viduals. Pain is the most common presentation as well as palpable masses, swelling, and limitation of motion.
Conventional imaging shows bone destruction and periosteal new bone formation.
A “sunburst” appearance, and soft tissue swelling is sometime seen. MRI imaging of the involved region is recommended because the MRI scan can then be used to plan resection and subsequent reconstruction. Arteriography is considered for limb salvage procedures. Chest x-ray and CT scan are used to detect metastatic disease in the lungs.
Technetium-99m or F-18 fluoride bone scans can outline the primary tumor, and FDG PET can detect unsuspected metastatic lesions.
History
19-year-old male with osteosarcoma of the left calcaneus. The current PET study is compared with the prior exam to evaluate response to chemotherapy.
Findings
There is again seen intense hypermetabolism in the body of the left os calcis (Figures 21.3B.1 and 21.3B.2). The tumor appears to involve all but the most posterior, supe- rior, and anterior portions of the calcaneus, roughly 80% with intense hypermetabo- lism. There appears to be extension into the soft tissues medially, laterally, and inferiorly. The relative intensity is similar to the prior exam (SUV=4.3 prior, 3.8 current) (Figures 21.3B.3 and 21.3B.4). No other hypermetabolic focus in the lower extremities is apparent. Incidental notation is made of interval appearance of treatment-related marrow hyperplasia (Figures 21.3B.5 and 21.3B.6) of the distal femora and proximal tibias. The torso exam is negative for metastatic disease.
Case 21.3B
FIGURE21.3B.1.
228 Part II Clinical Cases
FIGURE21.3B.2.
FIGURE21.3B.3.
FIGURE21.3B.4.
Impression
Persistent intense hypermetabolism of the left os calcis osteosarcoma, with no visible improvement since the prior exam. There is symmetric FDG uptake in bilateral neck, upper chest, and paraspinal area representing fat uptake.
Pearls and Pitfalls
• FDG PET is extremely valuable in monitoring patient response to chemotherapy, changing management in many patients considered surgical candidates.3,6
Discussion
Certain forms of chemotherapy may cause an apparent increase in or persistently high SUV value if images are obtained within the first few weeks to one month after treat- ment. Residual high uptake of FDG is most commonly due to poor response to treat- ment, but may also occur with development of an inflammatory reaction in the tumor bed, mimicking tumor progression or lack of treatment response. An additional short- term follow-up imaging study may help clarify whether there is response if immediate surgery or biopsy is not contemplated: persistent uptake after 2 to 3 months is more likely to reflect poor treatment response as inflammatory changes tend to subside over FIGURE21.3B.5.
FIGURE21.3B.6.
History
43-year-old female who has a history of right thigh angiosarcoma status post resection.
Her radiotherapy ended several months ago and is currently treated with chemo- therapy. The patient is being seen to evaluate for recurrence.
Findings
There is heterogeneous hypermetabolism in the upper medial aspect of the right lower extremity (Figures 21.4.1 and 21.4.2). The lesion extends from the surgical clips supe- riorly to the level of the medial femoral condyle inferiorly consistent with recurrent tumor. Mild to moderate bone marrow activity is also noted in the central skeleton (Figure 21.4.3).
Impression
1. Hypermetabolism in the right lower extremity suggestive of recurrent malignancy.
2. Central skeletal marrow hyperplasia consistent with chemotherapy-related marrow response.
Pearls and Pitfalls
• Prominent bone marrow activity is noted and explained by post treatment changes.3,6 230 Part II Clinical Cases
Case 21.4
FIGURE21.4.1.
time. In this case a third examination done 3 months after the first examination continued to demonstrate high tumor uptake, consistent with pathologically proven residual tumor.
FIGURE21.4.2.
FIGURE21.4.3.
Discussion
Angiosarcomas are a group of rare and high-grade tumors derived from vascular endothelial cells. Angiosarcomas frequently have been associated with previous irradiation sites. The prognosis of angiosarcoma is poor. The progression is frequently described as relentless. The standard approach is surgical resection. A few studies have reported limited success with adjunctive chemotherapy.
This patient has a right thigh angiosarcoma. Prior to PET, the patient had her right thigh mass resected followed by external beam radiation. Four months later, PET eval- uation was requested to evaluate for metastatic disease. The CT examination failed to detect any trace of residual disease. On the PET study, the recurrence was clearly visible.
232 Part II Clinical Cases
History
25-year-old male who has a history of a lateral right knee mass increasing in size. The patient is being seen to evaluate for extent of disease.
Findings
There is intense hypermetabolism in the popliteal fossa (Figure 21.5.1) corresponding to a mass on CT. There is also an additional site of hypermetabolism in the muscular compartment surrounding the proximal right tibia that is irregular posteriorly and con- fluent anterolaterally, corresponding to a large lobulated mass on CT. There are small high-density foci in the posterior aspect of the large mass which are curvilinear inferiorly, suggestive of calcifications within the wall of the lobules. A separate focally intense hypermetabolic lesion is noted more superiorly and posteriorly adjacent to the superior portion of the right fibula (Figure 21.5.2). There is some asymmetry in the surrounding vocal cord which may represents pharyngeal uptake and is physiologic.
Physiologic activity is seen in the heart, lung, liver, bowel, and testicles. No metastases are present in the lung.
Case 21.5
FIGURE21.5.1.
Impression
1. There is a large intensely hypermetabolic mass surrounding the right proximal tibia with additional satellite lesions adjacent to the right proximal fibula and in the popliteal fossa consistent with malignancy.
2. No evidence for distant disease.
Pearls and Pitfalls
• Synovial sarcoma is highly FDG avid because of the tumor’s inherent aggressive behavior.7,10
Discussion
In this patient, the histopathology was subsequently found to be consistent with syn- ovial sarcoma. Synovial sarcoma belongs to a group of sarcomas that usually grow by local extension, infiltrate adjacent tissues, and extend along tissue planes. Ninety percent of these sarcoma patients will have localized disease but the tumor eventually spreads to distant sites. More than 50% will develop disease in the lung as the first distant metastatic site. Chromosomal analysis, histology, and immunohistochemistry are some of the techniques available to identify the types of soft tissue sarcomas.
FIGURE21.5.2.
