Meralgia Parasthetica (MP) refers to a neuropathy of the Lateral Femoral Cutaneous Nerve (LFCN) which results in altered sensational over the anterolateral thigh.
Approximately 50% of LFCNs run through the substance of the inguinal ligament or through the tendinous Sartorius origin, whilst another 5% sit posterior to the ASIS and run over the iliac crest. These 3 types of nerve variants can be susceptible to mechanical trauma causing MP.
An easy way to find the nerve is to locate the ASIS and scan inferior to find the nerve lying superficial to the Sartorius muscle as shown above (FL-fascia lata, SART-Sartorius, TFL-Tensor Fascia Latae).
It can also be identified running superficial to the Iliacus muscle proximal to the ASIS.
Assess the nerve in transverse looking for any thickening of the nerve. A normal size is around 3mm2 in cross sectional area with abnormal considered anything over 5mm2. What we should be focused on is any significant change in cross sectional area.