Mushrooms in the valley

So, I’m back after 2 1/2 weeks away in the wilds of Yorkshire near the Gothic town of Whitby. It was quite a marvellous holiday with lots of mountain biking, body boarding and walking……but no Internet! This was both a tremendous relief as peace descended in the digital part of my brain, but also an interesting reminder of just how much we rely on digital access to stay in touch and to get things done. No worry though, despite my out of office messages I came back to >1500 emails, roughly 30 would be regarded as important…anyway. I could have written about repetitive strain injury to my delete button finger, but rather I am thinking back to the wonderful mountain biking in Dalby forest and the sort of injuries that I might have sustained whilst attempting the more difficult routes.

So enough of my Jollidays, back to medicine and possibly one of  my favourite diagnoses in the ED, I’m not sure why, possibly because I’ve seen quite a few in cyclists (and ED docs love cycling), but more likely I just like the name. I also think that is an under-diagnosed condition with clinical signs attributed to other conditions such as haematoma.

So what is it? Well, if you don’t know the name you might recognise the condition because I’ll bet you will have seen it at some point if you’ve been around the ED for a few years or so. A Morel-Lavallée lesion occurs when the superfical fat and skin separate from the underlying fascia to produce a potential space which then fills with fluid. These are often initially mistaken for simple haematomas but you can usually clinically distinguish them as they are more mobile, more ‘squishable’ and often demonstrate fluctuating size through the day as activity or posture changes. They are often tricky to spot in the early stages, and they may be missed on first presentation with signs becoming more obvious over days, weeks or sometimes months.

So, in the ED you might see this when a patient first comes to you having sustained a shearing injury with a subcutaneous swelling, but more likley you would suspect this injury in someone who returns days to weeks later with a persistent, fluctuant swelling that does not seem to be going away.

In the literature it is commonly described in relation to severe pelvic injuries, particularly those involving patients being run over where there are severe shear forces applied to the pelvic area and they are of particular concern to pelvic surgeons as they can interfere with operative management. I’m not so concerned with that group in this post as those patients will be heading to theatre under the care of the Orthopaedic surgeons. Rather I’m interested in those lesions that we might see and manage in the ED.

The separation of superficial tissues from fat requires a fairly significant shearing force that drags and tears the skin and fat from the underlying fascia. I guess that’s why we have seen in cyclists as the typical fall at speed, followed by an impact at an angle (as one hits the road or track) lends itself to this sort of injury. Typically they occur around bony protuberances such as the hip and knee as these are areas where the underling tissues are relatively fixed yet the skin is not. The advent of artificial pitches and hard surface playing environments may also be a factor, but that’s just my opinion, no evidence to back that up really…

The sort of crash that might cause this sort of injury is not uncommon in cyclists, particularly track cyclists, and as  Virchester is home to the greatest Velodrome in the world we have seen many riders from first timers right through to Olympic champions over the years. The description attributed to Sir Chris Hoy’s injury back in 2009 is of a Morel-Lavallée lesion and if you look at the footage from the crash you get a real idea of the shear forces involved in the injury mechanism. If you don’t watch the entire Kierin then skip to 2:50 & then slo-mo at 3:45 to see the crash.


There is also an absolutely fantastic personal account of a bicycle sustained M-L lesion on this blog by Fatheral, plus the blog has a great series of personal photos of what an M-L lesion looks like – although their lesion ended up with surgery (not always needed  – see below).

From Radiologia Brasilera

Although MR is advocated by radiologists as an optimal way of looking for these lesions I have found USS to be an excellent tool to define the nature and extent of these lesions. There are a few nice examples of what you see on USS in this paper from the Journal of Ultrasound Medicine, but you should be able to predict what you would see. A fluid collection superficial to the fascia that is easily compressible. Some good pics here as well. The one thing to think about when you are attempting ultrasound is that these are very ‘squishable’ so you can miss them if you are heavy handed. A very light touch may be needed to avoid ‘squashing’ the fluid away from your field of view.

So what to do about it? I have not found definitive advice on treatment but there appear to be a number of options.

So my personal plan with these lesions is, as always, dependent on the patient characteristics and size of the lesion. In patients with very small lesions then I would go for compression, particularly around the knee where compression is easy to achieve. For lesion around the hip it’s pretty difficult to get a compression bandage on in any effective manner so I tend to go straight for aspiration in those lesions, repeating on a daily or bi-daily manner under USS guidance. USS also gives you a really good idea of whether you are winning and if not then it’s a referral over to the surgeons for a vacuum drain.

So, a favourite diagnosis and although not common it is one that we can do something about and it’s got a great name….what more do you want 😉

….well, to be honest I’d like to see someone do a proper review of this lesion for the FCEM exam. I think it would make a great CTR.


Simon Carley


Further reading.

Also watch this excellent video from Radiopaedia

…and thanks to Nat for sorting my accents out 🙂


A Morel mushroom from wikipedia
A Morel mushroom from wikipedia


Cite this article as: Simon Carley, "Mushrooms in the valley," in St.Emlyn's, August 26, 2012,

8 thoughts on “Mushrooms in the valley”

  1. Seen several but did not know someone had claimed them. Bang Goes the Volans lesion again!
    Repeated aspiration for the large ones has been my practice and indeed they stop reattending. Whether that means it has cleared by that time or they have got bored coming remains unclear.
    I have got away with less than daily aspiration and indeed I have only had one to deal with since I got my sonosite(other US machines exist) so look forward to getting the feel with an US

  2. Hi Andy, there will be a Volans lesion out there somewhere (I suggest looking on the front of the forearm). You might be right about less than daily aspirations. I’ve not got enough experience and I’ve seen no trials to say otherwise.

    Quite good fun to do as well, and not usually painful for the patient either.

    USS at the time of aspiration certainly seems to help in order to get all the fluid out.


  3. I developed a Morel-Lavallée lesion following a traumatic cycling crash. I had it drained, but it has come back again and I couldn’t find any articles, apart from this one, that suggested further action. I’m certainly no medic, but I thought this was a very good and informative article which clearly describes what a Morel lesion is and suggests a plan of action to remove it. Good article and thanks for the insights.

  4. IGreat article.

    I have an MLL, had it since 6th July 2014 when I fell off my horse and broke my sacrum at S3 S4. I have had to fight for treatment of the MLL every step of the way. Mine started at 25cm by 7cm and orthopeadic consultants considered this to be small and not require intervention. I have had repeated aspirations and by February 2015 it was around 20cm by 31cm and infected. A plastic surgeon had agreed to a suction drain being inserted in January and then in Feb he inserted Tiseel glue into the cavity in the hope of sealing the cavity and preventing the return fo the MLL. In March I will undergo surgical debridement.

    My only bug bear is that the consultants did not listen to me, nor did they read any of the research I presented to them. There are quite a few research studies and case histories of MLLs out there so there is no reason that these should go untreated.

    A unique fact, I have had 7 litres of fluid drained from the MLL so far since 17th October 2014.

    UK orthopeadic surgeons really do need to be made more aware of available treatments!

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  6. Michelle Leibold

    I need help knowing what to do. I was in a terrible boating accident because of a drunk driver. I have developed MLL and my Doctor wants to do surgery but this will give me a14inch scar plus she said 50 % chance it’s going to come back. Please help trying to find a Doctor that specializes in MLL.

Thanks so much for following. Viva la #FOAMed

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