| Abstract|| |
Lipomas of the bone usually occur in the long bones and are seen in the fifth to seventh decade of life. Rib lipomas are rare and those having parosteal location are even rarer. We report a case of parosteal lipoma of the rib in a young male with some unique features. This is the fifth case of its kind to be reported in literature.
Keywords: Benign, bone, lipoma, parosteal tumors, rib, tumors
|How to cite this article:|
Sathe PA, Vaideeswar P. Unusual rib tumor: Parosteal lipoma with extensive osteochondromatous metaplasia. Indian J Pathol Microbiol 2008;51:525-7
|How to cite this URL:|
Sathe PA, Vaideeswar P. Unusual rib tumor: Parosteal lipoma with extensive osteochondromatous metaplasia. Indian J Pathol Microbiol [serial online] 2008 [cited 2019 Feb 18];51:525-7. Available from: http://www.ijpmonline.org/text.asp?2008/51/4/525/43749
| Introduction|| |
In general, tumors of the rib are infrequent  and most often metastatic. Most of the primary bone tumors or tumor-like lesions are usually intraosseous, but neoplasms can rarely be parosteal.  Parosteal bone tumors arise from the superficial cortex, the periosteum, or the periosteal soft tissues and these commonly include osteochondroma, chondroma, and chondrosarcoma. We report a rare parosteal lipoma of the rib seen as a pedunculated tumor in a young male.
| Case Report|| |
A 20-year-old male presented with a slow growing mass on the right side of his chest of 14 years duration. There was no history of pain or recent increase in size. A computed tomography (CT) scan of the chest (not available for review) had shown a large extrapleural tumor, measuring 4.8x3.3 cm arising from the anterior aspect of the right fourth intercostal rib. There was a central punctate cartilaginous matrix and calcification with peripheral soft tissue component. It revealed moderate homogeneous enhancement on post-contrast studies and indented the right costal pleura. Intra-operatively, the mass arising from the fourth rib was excised, along with a part of the rib. The post-operative course was entirely uneventful.
An ovoid encapsulated tumor measuring 5x3x2.5 cm was received with a 4 cm soft tissue tag attached to one of the poles [Figure 1]. The surface was shiny, light brown to yellow; the consistency was firm. The cut surface revealed central whorled, glistening, gray-white fibrous tissue and peripheral lobulated adipose tissue. A gritty sensation was felt in the center. These features could be identified in the CT scan of the tumor after excision [Figure 1], which was performed as radiological images of the patient were not available (patient lost to follow-up).
Cystic areas were not seen. A microscopy showed mature adipose tissue peripherally and the center composed of bands of hyalinized fibrous tissue [Figure 2] with foci of osseous and chondromatous metaplasia [Figure 3]. Nuclear pleomorphism, mitotic figures, or necrosis was not seen. A diagnosis of parosteal lipoma of the rib was given.
| Discussion|| |
We have described a tumor in a young patient for a prolonged duration that was composed of peripheral mature adipose tissue with central areas of predominant hyalinized fibrous tissue; amidst this were present foci of chondromatous and osseous metaplasia. Stout  coined the term mesenchymoma for tumors consisting of two or more mesenchymal elements, in addition to fibrous tissue; there is usually an admixture of such elements. However, owing to the characteristic pattern of arrangement of the different tissues in this case, we have diagnosed the lesion as a variant of a lipoma. A similar admixture of tissue can be seen in different, often long-standing rib lesions. These lesions form an important differential diagnoses and include mesenchymoma,  fibrocartilaginous mesenchymoma, and chest wall hamartoma.  The salient features are outlined in [Table 1].
Lipomas are the most common benign mesenchymal tumors that usually arise in soft tissues. Large, deep-seated, and/or long-standing lipomas are known to undergo metaplastic change (fibrous, cartilaginous, or osseous tissue) commonly occurring at a central location.  Lipomas arising in bones are rare with frequent intraosseous and uncommon parosteal location.  Parosteal lipomas comprise 0.3% of primary bone neoplasms and were first described by Seering in 1836. Since then, only about 150 cases have been reported. They occur most commonly in the long bones of adults in the fifth to seventh decades of life, with a wide age range of 3 to 84 years.  They present as painless, slow growing masses present for many years. Radiologically, one-third of the cases display no bony abnormalities. In the remaining tumors, there is a thickening of cortical bone, concave cortical erosion, and/or bowing of the bone. Pathologically, parosteal lipomas are well circumscribed, lobulated with a thin fibrous capsule and a broad based attachment to the bone or may possess a fibro-osseous pedicle. Osteochondromatous appearance is seen on radiographs, gross examination, and histology. The rib is an uncommon site and only four cases have been reported till date.  This is the fifth case of parosteal lipoma in the rib with few unique features. The patient was younger than the cases reported earlier. The tumor was adherent to the anterior surface of the rib by a fibrovascular pedicle, indicating a parosteal location and did not cause any rib abnormalities. Occasionally, disturbances in motor and sensory function of adjacent nerves may occur due to local pressure;  our patient did not have such symptoms. The abundant fibrous tissue metaplasia seen in our case has not been described in the earlier reports of parosteal lipoma in the rib.
| References|| |
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Pragati A Sathe
A/7, Jeevan Sudha Society, C.D. Barfiwala Road, Andheri (W), Mumbai 400 058, Maharashtra
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]