  We extend a well-known theorem by Jones and Makarov [JM] on the singularity
of boundary distortion of planar conformal mappings. We use a different
technique to recover the previous result and, moreover, generalize the result
for quasiconformal mappings of the unit ball $\B^n\subset \mathbb{R}^n$, $n\ge
2$. We also establish an estimate on the Hausdorff (gauge) dimension of the
boundary of the image domain outside an exceptional set of given size on the
sphere $\partial \B^n$. Furthermore, we show that this estimate is essentially
sharp.
  [JM] P. W. Jones and N. Makarov: Density properties of harmonic measure. Ann.
Math. 142 (1995), 427--455.
