A 6-year-old male with a past medical history of traumatic femoral fracture on the right side (Fig. 1) 4 years prior presents with new-onset pain in the same leg. There was associated leg length discrepancy and suspicion of a new fracture. Radiographs (Fig. 2) were performed in an outpatient practise and patient was referred to a pediatric orthopedic surgeon at our institution and an additional MRI was requested.
Femur radiograph at 2 years of age:
There is a comminuted spiral fracture of the shaft of the right femur with significant displacement of the fracture components (Fig. 1).
Femur radiograph at 6 years of age:
There is a completed healed old fracture of the right Femur with bony remodelling. There is the presence of a multilocular lucent lesion at the medial side of the right distal femur measuring 2 cm in maximum diameter (Fig. 2).
Femur MRI at 6 years of age:
MRI demonstrates a well-circumscribed lesion in the distal posteromedial femur metaphysis with a rim of low signal intensity due to a sclerotic margin (Fig. 3) and without soft tissue involvement.
Background
Cortical desmoid is a benign cortical irregularity [1] coined by Johnson et al in 1968 [2]. It is commonly found amongst 10-15-year-olds [3] in the posterior medial condyle of the femur [4] and is often asymptomatic in nature [3]. The pathophysiology of this lesion is thought to be due to stress and avulsion of either the medial head of the gastrocnemius or the insertion of the adductor magnus at the lateral aspect of the medial supracondylar ridge of the femur [5]. These lesions often have a fibrovascular appearance with intermixed spicules of bone [3]. Cortical desmoids are found most commonly in the left distal femur (2:1 ratio) and also have shown high bilateral prevalence in 35% of cases. More recently, the humerus has been found to be another common site of this type of lesion, with the pectoralis major and the deltoid muscle insertions being predominant sites of cortical irregularity [6].
Clinical perspective
Clinically, cortical desmoids are usually asymptomatic or present with very mild, non-specific pain [7,8]. They are often incidental findings on radiographs, however, are clinically important, as they may be mistaken for more aggressive processes such as osteosarcoma, chondroblastoma and infection [3]. The main differentiating factors between cortical desmoids and more aggressive lesions in the absence of a soft tissue mass in cortical desmoids [8], the lack of periosteal proliferation [7] and the common bilateral presence of lesions.
Imaging perspective
Plain radiographs are usually diagnostic for cortical desmoids, with lesions best seen on oblique views of the distal femur [3]. CT or MRI may add certainty to the diagnosis when radiographs are not definitive, however, they may also cause further diagnostic doubt in some cases [3]. Cross-sectional imaging can aid in confirming the lack of soft tissue involvement which could help reassure against an aggressive bone lesion [9]. Cortical desmoids have low signal intensity on T1-weighted MR imaging and an intermediate to high signal intensity on
T2- weighted MR with a rim of low signal intensity due to a sclerotic margin [10].
Outcome
The prognosis of a cortical desmoid is favourable with no requirement for any treatment. Supportive care should be given alongside limitation of activity if the lesion is causing pain. Whilst some lesions may persist into adulthood, they do not result in any functional disability or long-term sequelae [3].
Take-Home Message / Teaching Points
Cortical desmoids are one of the characteristic ‘do not touch‘ lesions.
The location of the lesion on the posteromedial side of the distal metaphysis of the femur is a hallmark that leads to the correct diagnosis.
Incorrect diagnosis may lead to unnecessary investigations and in some cases, false-positive malignant findings on biopsy may result in (sub-) total amputation of the limb.
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Cortical desmoid
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This case involves a 6-year-old male patient who underwent imaging due to recent onset of right femur pain (with a history of traumatic fracture). Current X-ray and MRI images show:
Overall, the imaging features are consistent with “cortical irregularity” or a “cortical desmoid,” without evidence of high-grade malignancy.
Based on the patient’s age, history of right femur fracture, and current imaging findings, the following preliminary and differential diagnoses are considered:
Considering the patient’s age (6 years), the typical location of the lesion (posteromedial distal femur), the imaging features (well-defined margins, lack of obvious soft tissue swelling, specific MRI signal characteristics), and clinical symptoms (mild pain with a previous fracture history), the most likely diagnosis is:
Cortical desmoid (also known as cortical irregularity or “pseudotumor”), a benign lesion.
This lesion is usually self-limiting and does not require invasive investigation or biopsy unless particular clinical circumstances arise (e.g., significant worsening of pain or worrisome imaging changes), where further follow-up or biopsy can be considered.
In the case of a cortical desmoid, no surgery or special treatment is typically necessary. Management is primarily conservative:
Disclaimer: The above report is based on the provided imaging and clinical history for analysis. It is for reference by healthcare professionals only and cannot replace an in-person consultation or a physician’s guidance. If any questions or changes in the condition arise, please seek medical attention promptly for individualized diagnosis and treatment.
Cortical desmoid
