Cortical desmoid

Cortical desmoids, also known as cortical avulsive injuries, Bufkin lesion or distal femoral cortical defects/irregularities, are a benign self-limiting entity that are common incidental findings. This is a classic "do not touch" lesion, and should not be confused with an aggressive cortical/periosteal process (e.g. osteosarcoma). 

Terminology

Cortical desmoid is a misnomer as this lesion does not histologically correlate to true desmoid tumors with more recent literature (c. 2020) ¹⁰ referring to these lesions as distal femoral cortical irregularities. 

Epidemiology

These typically present in adolescents (10-15 years of age). There may be a male predilection. 

Clinical presentation

Patients are usually asymptomatic and it is discovered incidentally. Occasionally pain may be present.

Pathology

Cortical desmoids are classically seen at the posteromedial aspect of the distal femur. They can be bilateral in ~33% of cases ⁴. They are related to repetitive stress at the attachment of the medial head of gastrocnemius or less commonly the lateral head of gastrocnemius distal or adductor magnus attachment sites ¹⁰.

Occasionally similar lesions have been described involving the humerus - medially at the insertion of the pectoralis major or laterally at the insertion of the deltoid ⁹.

Radiographic features

Plain radiograph/CT

Typically shows a saucer-shaped radiolucent cortical irregularity involving the posteromedial aspect of the distal femoral metaphysis at the attachment of the adductor magnus tendon. The lesion lacks an outer margin.

MRI

Defines anatomy much better and is seen as a cortically based lesion in the expected location (i.e. posteromedial distal femoral metaphysis) ^3,4,10:

• T1: low signal
• T2: high signal and surrounding low signal rim representing sclerosis may be present
• T1 C+ (Gd): most show enhancement

Nuclear medicine

On bone scan, there is an abnormal increase in activity because of the chronic stress/traumatic origin of this lesion.

Differential diagnosis

Imaging differential considerations include:

• fibrous cortical defect

Practical points

• cortical desmoid is one of the skeletal “don’t touch” lesions