Yes, mitral regurgitation leads to increase in pressure of right superior pulmonary vein and results in lung edema at the right upper zone, best regards..

If there is a high pressure in a pulmonary vein but normal pressure in the left atrium

Well there is a possibility of this happening if the left atrial incision is very close to the pulmonary vein orifices and during closure of the atriotomy there is some compromise of the pulmonary vein orifice leading to a situation akin to pulmonary vein stenosis; in that situation this may mimic a unilateral pulmonary edema and can be picked up on Chest X-ray and confirmed with an Echo assessment. Another possibility is if for some reason there is a clot occluding the Pulmonary vein orifice.

Hope this is helpful.

Can also be caused by a mitral regurgitrant jet being directed posterior and superiority, thus favouring the right PA, giving unilateral pulmonary oedema. There is a nice case report and X-ray in Chest, I think. Will have to look up the reference. 

Article Response to Letter Regarding Article, "Prevalence, Character...

I think manipulation and isolation of the lung during MICS mitral is the primary cause. Other anatomical causes are technical issues as described and should be avoided even in standard mitral operations. One approach is to have periodic ventilation of the lung and/or maintain a little PEEP. Less lung is manipulated in Aortic valves and you see less unilateral lung injury which I think is contusion more likely than pure edema. Hope this is helpful to all.

Minimally invasive right thoracotomy for mitral valve approach can be the cause of an edema of the right lung and finds its pathogenesis in: 1) mechanical factor or external compression of the right lung 2) altered pulmonary ventilation (lung perfused but not ventilated) 3) obstruction of the flow from the right superior pulmonary vein to the left atrium and 4) right phrenic nerve injury by careless handling.

Point 1 and 2 coexisting can cause edema of the right lung. During minimally invasive right thoracotomy for mitral valve, approach is always recommended to protect the right lung with a large gauze. The atelelettasia can be determined in a lung excluded from ventilation but still perfused from the bronchial arteries during cardiopulmonary bypass. It is always recommended to ventilate the right lung for the short time that has been excluded.

Point 3 is due to an error of left atrial incision during closure that determines iatrogenic stenosis of the right superior pulmonary vein. In this circumstance, there is an increase of the pressure in the pulmonary circulation with a risk of pulmonary edema. This event will be more frequent and acute when the pressure in the left atrium is lower. The patient cannot tolerate low pressures in the left atrium coexisting with normal size of the left chamber especially when there is an increase of pressure in the pulmonary circulation.

Point 4 is found with a chest RX showing a rise of right diaphragmatic dome. The patient has problems of respiratory failure and difficulty of extubation in the ICU

Yes  only thoracotomy can cause ipsilateral pulmonary edema. Pleural injury

Real syndrome. Jan 2015 Annals of Thoracic Surgery manuscript conclusion:

"Unilateral postoperative pulmonary edema after minimally invasive cardiac surgical procedures is common, carries significant morbidity, and has identifiable risk factors. Further research is needed to enable a better understanding of the pathophysiology and clinical implications of unilateral postoperative pulmonary edema."

http://www.annalsthoracicsurgery.org/issue/S0003-4975(14)X0012-3

Did you observe any change in ejection fraction from before the procedure? If not, I think is a worsening of heart failure. If EF increased after mitral valve surgery, perhaps a regurgitant jet is directed more to the right PVs.

narrowing of the right superior pul vein during closure of atriotomy incision

Unilateral right pulmonary edema has been reported both in sternotomy mitral cases and in right thoracotomy cases. I suspect that the main culprit is right pulmonary vein stenosis created during LA closure. One stitch is enough to make narrowing of PV. In addition, it is more difficult to watch the lumen of the right pulmonary vein during LA closure via right thoracotomy than via sternotomy.