Occult lipomatosis of the nerve as part of macrodystrophia lipomatosa: illustrative case

Abstract

BACKGROUND Macrodystrophia lipomatosa (MDL) is characterized by progressive overgrowth affecting soft tissues and bony structures and is part of lipomatous overgrowth syndromes. MDL has been associated with lipomatosis of the nerve (LN), an adipose lesion of nerve that has a pathognomonic magnetic resonance imaging (MRI) appearance as well as a mutation in the PIK3CA gene. The authors present a case of occult LN in the setting of MDL. OBSERVATIONS A 2-year-old boy with progressive soft tissue overgrowth of his proximal right lower extremity was initially diagnosed with neurofibromatosis type 1 (NF1). At our institution, NF1 as well as other overgrowth syndromes including PTEN hamartoma tumor syndrome were excluded. He was diagnosed as having so-called MDL. Upon reinterpretation of the patient’s MRI studies, short-segment LN involving the proximal sciatic nerve and part of lumbosacral plexus was identified. He underwent 2 debulking/liposuction procedures for soft tissue overgrowth. Genetic testing of tissue revealed a mutation in PIK3CA. LESSONS Thorough clinical examination (for signs of overgrowth) as well as an MRI study of the entire neural pathway is a critical part of the diagnostic workup to evaluate for LN. The authors believe that an increasing association of LN, even when occult, will emerge that will explain many cases with marked nerve-territory overgrowth.

Unrecognized sciatic lipomatosis of the nerve diagnosed by telehealth: illustrative case

“…As in our case, overgrowth is not always noted by the patient themselves or detected by physicians, especially in obese patients. A short-segment radiological finding of LN without known overgrowth can be easily missed; in contrast, it can be dwarfed by massive overgrowth associated with a large sciatic notch lipoma 14 or in the femoral nerve territory. 15 The presence of one notable abnormality can mask another important radiological finding (satisfaction of search) 16 ; for example, in our case the presence of the large sciatic notch lipoma left the associated LN undetected.…”

“…In the LS plexus and sciatic nerve, this can lead to bony changes such as lower limb lengthening, macrodactyly and exostoses, or osteochondromas and ankylosis; soft tissue changes include adipose proliferation, fatty infiltration, and lipomas. 12 , 13 Although nerve territory overgrowth can be dramatic (so-called macrodystrophia lipomatosa), 14 it can also be subtle. As in our case, overgrowth is not always noted by the patient themselves or detected by physicians, especially in obese patients.…”