|
The opinions and assertions contained herein are the private views of the authors, and are not to be construed as official, or as reflecting the view of the Department of the Air Force, Army, or Defense.
Key Words:
Heterotopic mesenteric ossification, pseudosarcoma, extraskeletal osteosarcoma.
Introduction:
Heterotopic Mesenteric Ossification (HMO) is a rare and distinct mesenchymal lesion. It typically has an intraabdominal location, usually occurs in males after surgery or abdominal trauma, and frequently presents with symptoms of intestinal obstruction. Herein we report a case of HMO.
History:
A 53-year-old taxi driver sustained multiple traumatic injuries in a high speed motor vehicle collision. He underwent resuscitative thoracotomy and open cardio-pulmonary resuscitation, followed by a midline laparotomy with splenectomy, partial small bowel resection, and repair of multiple mesenteric lacerations. The abdomen was left open due to high intra-abdominal pressure. He subsequently underwent multiple laparotomies for gradual abdominal closure. His recovery was complicated by an enterocutaneous fistula.
Radiology Studies
During the patient’s hospital course, multiple abdominal CT scans were obtained. As early as three weeks after surgery, thin, linear, branching high attenuation bands began to form within the small bowel mesentery (Figure 1). The attenuation of the bands was consistent with calcification. These bands radiated to the surgical defect in the anterior abdominal wall (Figure 2). Further radiologic findings are also shown. (Figures 3 & 4) (Video 1)
|
|
|
|
Figure 1 |
Figure 2 |
Figure 3 |
Figure 4 |
Procedure:
Approximately 10 months after the patient’s initial surgery, he returned to the operating room for adhesiolysis, small bowel (mid jejunum) resection, fistular resection, heterotopic bone resection, and Vicryl mesh closure.
Operative Findings:
Ossification of mesentery and serosa of small bowel at multiple foci with an enterocutaneous fistula.
Pathology:
The specimen submitted for pathologic examination consisted of an 11.0 cm segment of small bowel with a skin ellipse from the enterocutaneous fistula as well as adherent fibrofatty tissue with a thin calcified outer shell. In addition, there were six pieces of calcified tissue in the specimen jar, ranging from 7.0 X 5.0cm to 1.5 X 1.0cm in size. The histologic examination after decalcification of the specimen revealed well formed lamellar bone with periosteal fibrosis.
|
|
|
Figure 6 |
Figure 7 |
Figure 8 |
Discussion:
Heterotopic mesenteric ossification (HMO), also known as mesenteritis ossificans, intraabdominal myositis ossificans, and heterotopic ossification of the intestinal mesentery, can be defined as an intraabdominal reactive change that presents as a distinct pseudo tumor. It can be considered as part of the group of rather rapidly occurring, bone forming pseudo tumors. Myositis ossificans is the classic prototype of this group and occurs in soft tissue following trauma. Patients who develop ossifying pseudo tumors may have a have genetic predilection for this condition. HMO occurs predominantly in male patients as sequela to abdominal trauma or multiple abdominal surgeries. Intestinal obstruction is a common presentation.
Heterotopic ossification refers to the formation of bone in normally non-ossifying tissues. The mechanism by which this occurs is not clearly known but it may be secondary to osteoblastic metaplasia of mesenchymal cells or traumatic and/or surgical implantation of bone or periosteum in soft tissues1. It differs from dystrophic calcification, which is defined as calcium deposition without osteoblastic activity and usually occurs in the gastrointestinal tract in association with mucin producing tumors2. Although it can be speculated that HMO represents ossification in some cases of sclerosing mesenteritis, the latter does not show gender predilection and is a diagnosis of exclusion, occurring spontaneously without antecedent trauma or surgery3. Furthermore, HMO can recur4. It can be hypothesized that HMO is an exuberant reaction to trauma in a predisposed individual5.
The gross appearance of the specimen varies from firm to hard foci with areas of fat necrosis in the fibrofatty tissue. Although bowel obstruction is a common presentation, infiltration of bowel wall is not seen. The histologic examination reflects the gross appearance and can show areas of fat necrosis, hemorrhage, cellular spindle cell proliferation, areas of fibrosis, and osteoid formation with or without chondroid. A zonation pattern reminiscent of myositis ossificans in soft tissues with central fat necrosis surrounded by myofibroblastic proliferation, mitotically active chondroid and peripheral zones of ossification (the latter is characterized by a lace-like osteoid, typical of reactive processes), is typically seen. This is in contrast to the “reverse zonation” characteristic of extraskeletal osteosarcoma, where the mature cells occur in the center of the lesion6. However, in patients with very short history, the zonation pattern may not be appreciated. In long standing cases, mature bone with marrow may be present. Although HMO is a proliferative lesion, pleomorphism and bizarre nuclear forms are not usually exhibited7. Atypical mitotic figures and coagulative tumor necrosis are also not seen in HMO, and their presence should raise the suspicion for extra-osseous osteosarcoma.
References
1. Kaplan FS, et al. Heterotopic Ossification. J Am Acad Orthop Surg 2004; 12:116-125.
2. Haque S, et al. Heterotopic bone formation in the gastrointestinal tract. Arch Pathol Lab Med. 1996 Jul;120(7):666-70.
3. Emory TS, et al. Sclerosing mesenteritis, mesenteric panniculitis and mesenteric lipodystrophy: a single entity? Am J Surg Pathol. 1997;21:392-398.
4. Myers MA, et al Heterotopic ossification within the small-bowel mesentery. Arch Surg. 1989 Aug;124(8):982-3.
5. Wilson JD, et al. Heterotopic mesenteric ossification ("intraabdominal myositis ossificans"): report of five cases. Am J Surg Pathol 1999;23:1464 -1470.
6. Weiss SW, Goldblum JR, Enzinger and Weiss's Soft Tissue Tumors. 4th ed. St Louis: Mosby, 2001.
7. Patel RM, et al. Heterotopic Mesenteric Ossification. A Distinctive Pseudosarcoma Commonly Associated with Intestinal Obstruction. Am J Surg Pathol 2006;30:119-122.
8. Zamolyi RQ, et al. Intraabdominal myositis ossificans: a report of 9 new cases. Int J Surg Pathol. 2006 Jan;14(1):37-41.
|
