Myositis ossificans

Myositis ossificans (MO) and fibro-osseous pseudotumour of digits are localised self-limiting lesions composed of reactive hypercellular fibrous tissue and bone (1). They often grow rapidly and biopsy may reveal mitotic activity and hypercellularity, and they are therefore classic pseudosarcomas.

These conditions can occur throughout life, but are most common in young adulthood (mean age 32 years). Males are more frequently affected than females (3:2), although FP more commonly occurs in females.

Soft tissue injury is the most common initiating event. MO can develop anywhere in the body but is most common in areas which are readily injured, such as the extremities, thigh, buttock and shoulder. It usually develops in skeletal muscle. Similar lesions occur in the subcutaneous tissue (panniculitis ossificans), tendons or fascia (fasciitis ossificans).

Early in the development of the lesion, there is classically swelling and pain. Calcification appears after 2-6 weeks, often in an eggshell like-distribution (hence the synonym myositis ossificans circumscripta). Over time, lesions become hard and well demarcated.

Lesions range in size from 2 to 12cm with a mean of around 5cm. Macroscopically they have a gritty white periphery and a soft tan haemorrhagic centre. On microscopy, early lesions appear highly cellular, comprising proliferating fibroblasts. There can be well-formed bony trabeculae peripherally.

Treatment is usually expectant with anti-inflammatory medication. Lesions can be removed after they have matured. Recurrence is unusual. The use of bisphosphonates has been described (2).

 

1. WHO Classification of tumours of soft tissue and bone. 4th Edition. 2013

2. Mani-Babu S et al. Quadriceps traumatic myositis ossificans in a football player: management with intravenous pamidronate. Clin J Sport Med. 2014 Sep;24(5):e56-8

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Sacrectomy

Sacrectomy is a challenging surgical procedure used in the treatment of primary tumours of the sacrum (eg chordoma) or rectal tumours (usually locally recurrent) involving the sacrum. The complexity and disability associated with the procedure depends in large part on the level of resection. High sacral resections can lead to loss of bladder and bowel function (1).

The procedure can be performed through a combined abdomino-lateral approach, sequential abdominal then posterior approaches or entirely by a posterior approach depending on the local extent of the tumour and involvement of critical anatomical structures. Division of the bone just below the lower border of S3 preserves sphincteric function. Bilateral sacrifice of S2-S4 roots lead to urinary and faecal incontinence and male impotence. Anorectal incontinence can be preserved if one S2 root is maintained.

The dural sac ends at the S2/3 junction, and if entered, requires meticulous closure. For higher sacral resections the posterior sacral plate is removed with rongeurs, which may allow identification of sacral nerve roots. Attempts should be made to spare the pudendal nerve if it is encountered running posterior to the ischial spine.

Sacrectomy requires specialist expertise and a team which includes colorectal, orthopaedic and plastic surgical expertise as appropriate. After resection of the sacrum, reconstruction of the soft tissue defect may be achieved using a VRAM rectus abdominis pedicled flap or IGAP gluteal muscle transfers.

For more information, the chapter on sacrectomy in Malawer’s book is very helpful (http://www.sarcoma.org/publications/mcs/ch27.pdf).
1. Spine J. 2015 Feb 1;15(2):222-9. Maintenance of bowel, bladder, and motor functions after sacrectomy. Moran D, Zadnik PL, Taylor T, Groves ML, Yurter A, Wolinsky JP, Witham TF, Bydon A, Gokaslan ZL, Sciubba DM.

Dedifferentiated liposarcoma

A dedifferentiated liposarcoma is a soft tissue tumour which shows progression either in the primary tumour or after local recurrence to a sarcoma of variable histological grade, often not lipogenic. Dedifferentiated liposarcoma occurs in up to 10% of well-differentiated liposarcomas, although the risk is higher in the retroperitoneum and lower in the extremities, likely reflecting the longer time taken to detect tumours in the former location.

Dedifferentiated liposarcomas are most common in the retroperitoneum, but can occur in the spermatic cord or rarely head and neck and trunk. They are extremely rare in subcutaneous tissues. These tumours usually present as a painless mass, with both lipomatous and non-lipomatous elements on MRI scanning. Some present with an increase in size of a long-standing tumour, suggestive of dedifferentiation.

Dedifferentiated areas are variable histologically, but can resemble undifferentiated pleomorphic sarcoma or myxofibrosarcoma. Tumours most often contain ring or giant marker chromosomes.

After treatment, local recurrence can occur in up to 40% of cases, particularly in the retroperitoneum. Tumours exhibit a less aggressive clinical course than other types of high grade pleomorphic sarcoma, with metastases in 15-20% of cases and a overall mortality of 28-30% at 5 years.

 

1. WHO Classification of Tumours of Soft Tissue and Bone. 4th Edition, 2013.

Atypical lipomatous tumour

An atypical lipomatous tumour is a locally aggressive mesenchymal neoplasm in which the adipocytes show significant variation in cell size and have some nuclear atypia. These tumours are at risk of local recurrence. In the extremities or trunk the term atypical lipomatous tumour is justified as complete excision is usually curative and local recurrence manageable. In the retroperitoneum or mediastinum however, tumours with the same biological composition are difficult to completely remove and can recur with disastrous consequences for the patient. In these locations, the term “well-differentiated liposarcoma” may therefore be more appropriate.

Atypical lipomatous tumours account for 40-45% of all liposarcomas and occur predominantly in middle aged adults, peaking in the sixth decade. They most frequently occur in the deep soft tissues of the limbs, especially the thigh, but may also occur in the retroperitoneum or paratesticular area. Tumours often grow slowly, are painless and can achieve significant sizes.

Anatomical location is the most important prognostic factor. Lesions in surgically resectable sites tend not to recur after complete excision. In more difficult anatomic sites, incomplete excision is associated with local recurrence, which in turn can lead to loss of local control, or be associated with dedifferentiation and death. The risk of dedifferentiation is said to be over 20% in the retroperitoneum, but <2% in the limbs.

1. WHO Classification of Tumours of Soft Tissue and Bone. 4th Edition, 2013.

Lipoma

Lipomas are benign soft tissue tumours composed of mature adipocytes. Lipomas are the most common mesenchymal tumour in adults and are most common between the ages of 40 and 60 years. 5% of patients have multiple lipomas.

Lipomas typically occur in the subcutaneous soft tissues, but can also present in deeper locations, for example within or between muscles, or on the surface of bones.

Lipomas usually present as a painless soft tissue mass. On histological examination they can contain bone (osteolipoma), cartilage (chondrolipoma) or fibrous tissue (fibrolipoma). Deep intramuscular lipomas often encase muscle fibres – this can be seen on MRI scanning and these tumours have a higher rate of local recurrence.

Angiolipoma is a lipoma variant containing small capillary walled vessels. 5% of cases are inherited as an autosomal dominant. These usually present as tender subcutaneous masses. Angiolipomas are always benign and show no tendency to recur.

A large lipoma with stranding of muscle fibres

A large intramuscular lipoma of thigh with stranding caused by muscle fibres

1. WHO Classification of Tumours of Soft Tissue and Bone, 4th Edition.

 

Information for patients:

A good summary from NHS Choices.