MSK Case 3: Parosteal Osteogenic Sarcoma

Igor Mikityansky MD, MPH and Johnny U .V Monu, MD

Imaging Sciences URMC 2008
Publication Date: 2009-06-04


A 21-year-old male presents for work-up of a knee mass that developed after arthroscopy for knee pain and biopsy. Patient’s pain has been worsening for over 3 years. A year and a half prior to presentation, he underwent arthroscopic knee surgery in an outside hospital, but continued to experience pain and swelling. Several weeks prior to presentation he underwent bone biopsy of a mass in the same hospital.

Examination of the lower extremities demonstrated diffuse swelling of the left knee region with an incision along the antero-lateral aspect of the distal thigh with small amount of serous drainage in the mid portion. A soft and compressible lobule of swollen tissue was felt just underneath the skin, perceived to be filled with fluid. Limited range of motion to flexion of 90 degrees and a very large joint effusion were noted.


Radiographs demonstrate large intra-articular irregular ossified masses in suprapatellar and infrapatellar locations associated with moderate joint effusion. The superior lesion demonstrates incomplete lucent cleavage plane between the lesion and the periosteum. A subtle band of dense tissue is seen extending into anterior-lateral distal femoral diaphysis.

MRI images demonstrate enhancing low T1 weighted-image and intermediate to high T2 weighted-image signal mass anterior to distal femoral metaphysis with evidence of cortical breakthrough. A second mass with similar characteristics is visualized within the Hoffa’s fat pad without attachment to the osseous structures. A large joint effusion is also noted. A low T1-weighted signal elongated abnormality is seen under the endosteum extending into the distal femoral diaphysis corresponding to the area of sclerosis seen on the plain film


The gross pathologic examination revealed a 4 x 6 x 1.5 cm well-circumscribed, tan, firm, smooth, nodule on the anterior-lateral body of the distal femoral surface. Invasion of cortical and invasion of trabecular bone were noted superior to this nodule. The trabecular bone extension measured 2.5 cm long and 1.1 cm in maximum thickness and appeared on gross examination as cortical thickening. Articular capsule lining had smooth, cloud-like matrix pattern, ranging from tan to red-gray. A 4.5 x 3 x 3 cm smooth, ovoid, tan mass was also described in the fat pad and a 1.3 x 1 x 1 cm well-circumscribed, smooth, round nodule was found on the medial articular capsule lining. A 0.2 cm cartilaginous capsule was described at the periphery of the lesions.


Parosteal Osteogenic Sarcoma


Parosteal or juxtacortical osteogenic sarcoma is a low grade malignancy more common than either periosteal or high grade conventional osteosarcomas occurring on the surface of the bone [1]. It represents up to 65% of surface osteosarcomas [2]. Typically it presents in the third or fourth decades and has better prognosis than conventional osteosarcoma unless the tumor undergoes dedifferentiation [2]. In 65% of cases it is located on the posterior surface of distal femoral metaphysis [1, 3, 4]. Less commonly it occurs in humerus (15%), tibia (10%), fibula (3%), radius (2%), or ulna (1%) [1]. A palpable mass is seen in 80% of cases [4]. Dull, aching pain and joint dysfunction are seen in 59% and 17%, correspondingly [4].

Gross examination demonstrates lesion arising from the periosteal tissue with mature bone and small areas of fibrocartilage [4]. Microscopic examination reveals fibrous stroma surrounding irregular osseous trabeculae [1]. Usually the periphery is more cellular and the base demonstrates thicker and denser trabeculae and more collagenous fibrous component [4]. In 50 to 80% chondroid islands are seen [1]. Occasionally, a small focus of dedifferentiated or conventional osteosarcoma may be found within parosteal lesion [1,2]. Dedifferentiation reportedly occurs in one-fourth to one third of parosteal osteosarcomas [5]. They can be detected after the first recurrence and frequently are synchronous [5]. Extension into medullary cavity carries increased risk of pulmonary metastasis [4]. In addition, higher surgical grade increases risk of recurrence [4]. Parosteal osteogenic sarcoma extends into medullary cavity in one-third of the cases and metastasizes in 5% of cases [2, 5]. Likelihood of medullary cavity involvement correlates with duration of the symptoms at presentation [4]. In addition, Grade I tumors (abundant collagen, rare mitosis, slight increase in nuclear pleomorphism, hyperchromaticity, and hypercellularity) do not metastasize, while grade 2 (less collagen, slightly increased hypercellularity, large, slightly pleomorphic and hyperchromatic nuclei, more frequent mitosis) and 3 (hypercellularity, numerous mitosis and hyperchromatic, pleomorphic nuclei) lesions metastasize only after medullary cavity extension [4]. Dedifferentiated lesions are associated with medullary invasion in two-thirds of cases and metastasis in one-third [5]. In contrast, high grade surface osteosarcoma metastasizes in 50% of cases [5]. The mortality of dedifferentiated osteosarcoma reportedly approaches mortality of high grade surface osteosarcoma, which is 50% [5]. This may be related to its very poor response to chemotherapy [5].

On imaging, a large, sessile, lobular, radiodense mass arising from the external cortex via a pedicle and separated by a radiolucent cleft is usually seen [1,3]. In the late stages it surrounds the bone [1]. Characteristic ossification proceeds from the center to periphery [1]. The foci of dedifferentiation usually appear as ill-defined unmineralized areas of soft tissue density with intermediate T1-weighted and high T2-weighted MRI signals [2]. On angiography, they are usually associated with hypervascularity [5]. These areas should be targeted during either needle or excisional biopsy [5]. Bone scan demonstrating dense uptake in the lesion can define extent of the lesion and allow surgical planning [4].

The differential diagnoses of parosteal osteosarcoma include myositis ossificans, sessile osteochondroma, synovial sarcoma, and occasionally osteoma [1]. Myositis ossificans usually is associated with history of a mass appearing after trauma [1]. Usually there is a complete lucent line separating the mass from the bone [1,3]. The ossification progresses from periphery to the center [1]. Ostochondroma demonstrates continuous cortex and medullary space coverage [1]. In addition to visualization of cartilaginous cap on MRI, chondroid calcifications may be seen in the cap on plain radiographs [2]. Synovial sarcoma demonstrates juxtaarticular soft tissue mass with amorphous calcifications in 25 to 30% [6]. Periarticular osteoporosis is frequently seen [6]. Periosteal reaction, invasion of cortex, and massive bone destruction are rare [6]. Osteoma is usually more dense and homogeneous than parosteal osteosarcoma [6].

The prognosis for parosteal osteosarcoma is usually better than for the conventional and periosteal osteosarcoma [3,4]. A wide margin surgical resection is usually the treatment of choice for grade 1 as well as grade 2 and 3 lesions without medullary cavity extension [4]. If freely movable, the adjacent neurovascular structures are dissected away from the fibro-fatty plane [4]. Otherwise, en bloc excision with vascular reconstruction are performed to avoid local recurrence [4]. Grade 3 lesions with medullary cavity involvement require adjuvant chemotherapy [4]. However, presence of dedifferentiated osteosarcoma significantly worsens the prognosis [5]. Satellite lesions are seen in recurrent lesions presumably due to seeding, but have not been described in untreated parosteal osteosarcoma [4].

Our case was managed with left knee joint resection and reconstruction using tibial and patellar allograft, left rotating hinge Biomet type distal femoral and total knee replacement, reconstruction of left quadriceps with latissimus free flap procedure. The microscopic examination of the removed bone demonstrated three foci of parosteal osteosarcoma with varying degree of cartilaginous tissues. The seeding due to prior arthroscopy and/or biopsy was considered to be the cause of multifocal disease. The patient is being followed by the medical oncology in order to evaluate for need of the adjuvant chemotherapy.


We appreciate the assistance of Dr. Xi Wang who helped us with pathologic images for the case.


  1. Resnick D. Bone and Joint Imaging. 1st ed. Philadelphia: W.B. Saunders Company; 1989.
  2. Suresh S, Saifuddin A. Radiological appearances of appendicular osteosarcoma: a comprehensive pictorial review. Clin Radiol. Clin Radiol. 2007 Apr;62(4):314-23. [PubMed]
  3. Burger FA, Kormano M, Pudas T. Bone and Joint Disorders: Differential Diagnosis in Conventional Radiology. New York: Georg Thiem Verlag; 2006.
  4. Campanacci M, Picci P, Gherlinzoni F, Guerra A, Bertoni F, Neff JR. Parosteal osteosarcoma. J Bone Joint Surg Br. 1984 May;66(3):313-21. [PMID: 6586725]
  5. Bertoni F, Bacchini P, Staals EL, Davidovitz P. Dedifferentiated parosteal osteosarcoma: the experience of the Rizzoli Institute. Cancer. 2005 Jun 1;103(11):2373-82. [PMID: 15852358]
  6. Stoller DW, Tirman PFJ, Bredella MA, Beltran S, Branstetter RM, Blease SCP. Diagnostic Imaging: Orthopedics. 1st ed. Altona: Amirsys; 2004.

36 images