Teaching Case

A 41-year-old man underwent emergent exploratory laparotomy after left hypocondrium penetrating trauma, which showed hemoperitoneum with gastric perforation, transverse mesocolon laceration and inferior mesenteric artery section.
During a long postoperative period the patient developed persistent symptoms of intestinal obstruction that led to several CT and a relaparotomy.

On 7th-day patient developed abdominal distension and recurrent vomiting. CT performed on 12th-day (Fig.1) revealed gastroduodenal obstruction with transition point in proximal jejunum.

Given the lack of improvement surgery was performed on 18th-day. Re-laparotomy revealed multiple hard, stony adhesions over previous surgical bed.

Persistent intestinal obstruction symptoms led to a new CT on 35th-day (Fig.2) that showed findings consistent with heterotopic mesenteric ossification. Due to the technical difficulties in the previous surgery, a conservative management course was pursued through total parenteral nutrition, bisphosphonates and steroids. Progressive clinical improvement was observed, and oral tolerance was successfully reintroduced on 42nd-day. The patient was discharged in good condition on 60th-day.

Follow-up CT (Fig.3) 11 months after showed progression of ossification with extensive formation of cortical and trabecular bone in previously affected areas, although the patient had remained asymptomatic. He was followed up as an outpatient without complications after 3 years (Fig.4).

Heterotopic ossification (HO) is the formation of bone in the soft tissues. Heterotopic bone formation in mesentery is an extremely rare form of HO with approximately 50 reported cases in the literature.[1] The ossification of the abdominal scar is more common than heterotopic mesenteric ossification (HMO), although the incidence of these entities is unknown.

The pathophysiology of HO is not well established, although it has been postulated to be due to osteoblastic metaplasia of multipotent mesenchymal cells in response to severe inflammatory stimulus due to trauma, or occasionally it can also be due to traumatic or surgical implantation of bone or periosteum into the soft tissue.[2]

HMO occurs predominantly in men, usually in mid to late adulthood. In nearly all of the cases described, abdominal surgery or trauma preceded HMO and most patients present with bowel obstruction or fistula, [3] although asymptomatic cases have been reported.[1]
The time frame from initial injury to heterotopic bone formation is unknown. The clinical symptoms usually appear 2 or 3 weeks after abdominal trauma or surgery (range, 4 days to 2 years). [4]

Radiologically, HMO characteristically manifests in its early stages as multiple linear and branching, high attenuating structures within the mesentery and omentum. Over time these high-attenuating structures mature into bone with a discernible trabecular and cortical architecture, often with central fatty marrow. Many of these lesions displayed a “wishbone” or “bird’s foot” morphology. [5] Recognition of this finding allows a confident and accurate diagnosis of HMO. It should be differentiated from other entities such as oral contrast leakage, active extravasation of intravascular contrast from bleeding vessels, retained surgical material and dystrophic calcification within mesenteric neoplasms, particularly mucinous neoplasms and carcinoid tumours.[5]

Because HMO is a rare entity, the optimal treatment strategy is not established. In asymptomatic cases, watchful waiting is recommended. Surgical intervention is reserved for symptomatic patients because of the concern that HO will recur and possibly worsen with repetitive surgery.[6] Besides, surgical intervention with complete excision of ossified tissue has been shown to be associated with significant morbidity and mortality.[7] Pharmacologic agents including nonsteroidal anti-inflammatory drugs (NSAIDs, in particular indomethacin), bisphosphonates, or even radiotherapy after surgery have been used to reduce local recurrence.[6] In our case, the conservative treatment including bisphosphonates and steroids successfully solved the intestinal obstruction, avoiding another surgical operation, but heterotopic ossification continues progressing.

Written informed patient consent for publication has been obtained.