Serve static files from same dir as rendered file express

I have the following middleware for static files defined in express:

app.use(express.static(__dirname + '/public'));
app.use('/lessons', express.static(__dirname + '/lessons', { redirect : false }));

Inside lessons folder I have a couple of lesson folders

lessons
|-- lesson01
|-- lesson02
.
.
.

Inside every lesson folder there's a lesson.md file that I render. This file has references to images in the same lesson folder. I want to be able to just use for example img01.png inside the markdown file to reference the image, but express expects the image to be found in /lessons/img01.png and not in /lessons/lesson01/img01.png.

Using ./img01.png as a reference to the image in the markdown file didn't help either.

Any idea on how yo tell express to look in the same directory for the static file ?

Thanks

Edit :

A little more info,

The route to get the lesson file is :

app.get('/lessons/:name', function(req, res, next) {
    res.locals.controller = 'lessons';
    var name = req.params.name;
    var lesson = lessons[name];
    if (!lesson) {
      return next();
    }
    lesson.path = 'lessons/' + name;
    lesson.file = lesson.path + '/' + name + '.md';
    markdown(lesson.file, function(result, err) {
      if (err) {
        console.log(err);
      }
      lesson.body = result;
      res.locals.lesson = lesson;
      res.render('lesson');
    });
});

Also, I am using middleware called connect-slashes to remove the slash from the end of each URL. (As result of this SO question)

var slashes = require('connect-slashes');
var app = express();
app.use(express.static(__dirname + '/public'));
app.use('/lessons', express.static(__dirname + '/lessons', { redirect : false }));
// add middleware to remove trailing slash in urls
app.use(slashes(false));