Spontaneous dissection of coeliac and superior mesenteric artery: double whammy

Discussion

Isolated and spontaneous coeliac and SMA dissections without any involvement of the aorta is an exceptionally rare condition. In order of higher to lower incidence rate, arterial dissection can occur in the renal, coronary, cerebral, carotid, vertebral, and visceral arteries.3

Coeliac and SMA dissections are commonly seen in middle-aged men. They usually appear with acute or chronic epigastric or upper left abdominal pain which may be postprandial in nature. Other accompanying symptoms can be nausea, vomiting and diarrhoea.3 4

Approximately 50% of patients are asymptomatic and incidentally diagnosed on imaging; occasionally, they present with splenic infarction, intestinal angina or haemorrhage.3 5

Common risk factors are atherosclerosis, trauma, iatrogenic related to interventions, pregnancy, syphilis, fibromuscular dysplasia, polyarteritis nodosa (vasculitis), cystic medial degeneration, Marfan syndrome, Ehlers-Danlos syndrome, etc.3 5

Hypertension is commonly prevalent among these patients, but no direct cause–effect relationship with hypertension had been established. Hypertension is more commonly associated when mesenteric arterial dissection involves the aorta. Park et al noted high blood pressure in 66% patients of aortic dissection, while only 31% in isolated mesenteric artery dissection.6

The exact pathogenesis of spontaneous mesenteric artery dissection is still unknown. The study showed that the dissection typically spares the ostium and starts 1.5–3 cm distal from the orifice of SMA.7 Park et al proposed that a part of SMA at the lower border of the pancreas is relatively mobile compared with the proximal fixed part, causing abnormal ‘shear stress’, leading to injury and dissection.6 Park et al reviewed CT scans of 51 patients and observed that dissection usually starts at the anterior wall of the convex part of the SMA.2 With the help of simulation software, he inferred abnormal haemodynamic factors causing mechanical shear stress responsible for this dissection.6

Ultrasound with colour doppler, CT angiogram, MR angiogram and catheter-based angiography are the imaging modalities available for diagnosis. Ultrasound has low sensitivity but is a useful tool in the hands of an experienced operator. Emergency ultrasound scans by an inexperienced operator may miss the dissections which may be the reason for a ‘normal’ USG scan in our case. Moreover, the patient may have abdominal pain if a probe is placed deeply. CT angiography (early arterial phase) is the most preferred imaging modality in this setting and provides excellent images showing intimal flap, true and false lumen, and extent of the dissection but involves radiation exposure and contrast use. The delayed arterial phase is used to evaluate acute extravasation of blood or vascular malformation or aneurysmal disruption. Also, the portal venous phase of contrast-enhanced CT can show mesenteric or portal venous gas associated with bowel necrosis which is highly specific for acute mesenteric ischaemia. It is also cheaper compared with MR angiogram and invasive angiogram, hence can be used for serial imaging for follow-up also. MR angiogram can be used in patients in whom contrast must be avoided but the procedure is relatively longer and more expensive compared with CT angiogram and has a limited role in evaluating distal arterial stenosis and non-occlusive mesenteric ischaemia. Catheter-based angiography is the gold standard method but invasive, more expensive and requiring more radiation, hence usually considered when intervention such as balloon angioplasty, stenting, coil implantation or embolizsation is planned in the same setting.2 3 5

D-dimer is a highly sensitive early marker for acute thromboembolic mesenteric ischaemia, but specificity is low. Therefore, it may be useful for the exclusion of this diagnosis if clinical suspicion is not high. However, no specific cut-off value for diagnosing acute mesenteric occlusion has been given in published literature. One of the imaging modalities is necessary to confirm the diagnosis even if the levels are high.8

Usually, the collateral connection exists between the coeliac artery and the SMA mainly via the inferior pancreaticoduodenal artery. So, when either coeliac or SMA is affected with flow-limiting dissection, distal flow is maintained via these collateral circulations. However, in our case, both coeliac and SMA had non-occlusive dissection. Hence this patient was at higher risk of mesenteric infarction as collaterals might not provide enough blood supply to the distal bowel segment. Such patients require close follow-up for ischaemic complications.

There is no clear evidence-based guideline for the management of visceral arterial dissection. Treatment for uncomplicated cases includes hypertension control, antiplatelets or anticoagulants, whereas for complicated cases visceral artery stenting or open surgical exploration or hybrid approach is recommended.1 Reports have been published for both conservative management1 4 9 and invasive interventions.2 Asymptomatic or clinically stable patients best respond to medical therapy.4 Anticoagulation is preferred over antiplatelets as it decreases the thrombotic risk in presence of uncovered subendothelial tissue factor.9 It has been used for up to 6 months, thereafter no proven beneficial role. Beyond this period, or if there is any worsening or persistence of the symptoms, one should consider invasive or surgical management. Traditionally, vitamin K antagonists like warfarin have been used in this setting. However, non-vitamin K antagonist oral anticoagulants (NOAC) can be a good alternative as a regular blood test to maintain INR in the therapeutic range is not needed. However, no clear guideline is available for using NOAC in such conditions. Our patient received warfarin therapy because he could not afford the more expensive NOAC therapy.10 Antiplatelet therapy has been advised by some authors during the acute stage of spontaneous dissection. Because exposure to denuded subendothelial tissue can provoke thrombosis. Future risk of extension of dissection can be minimised by strict blood pressure control.11

Patients who have worsening abdominal pain and tenderness or haemodynamically instability with drop in haematocrit value, one must rule out ongoing dissection, aneurysm formation, haemorrhage or ischaemic bowel.5 Endovascular stent graft placement is indicated in these conditions.5 7 Benefits of percutaneous angioplasty over open surgery include early ambulation and early discharge from hospital, less need of serial CT scan, less need for anticoagulants and less procedure-related complications. Potential risk includes stent thrombosis, restenosis and procedure-related complications. Balloon fenestration or selective arterial embolisation is an alternate approach.5 No published data support the superiority of either treatment. However, very few cases are reported to date and longer follow-up periods are required for any definite conclusions.

Surgery is indicated when the patient has persistent or recurrent abdominal pain, uncontrolled hypertension, hypotension or multifocal lesions, rupture of artery, aneurysm rupture. It includes resection of the dissected segment with anastomosis, aortomesenteric bypass, interposition graft, thrombectomy and intimectomy–patchplasty.2 3 Surgery also allows to take a biopsy of an affected artery to rule out vasculitis as a cause of dissection.7