6b (Ankle) - Answer: 10-year-old female presents with medial right ankle pain

HISTORY: 

This 10-year-old female presents with medial right ankle pain after jumping.


(QUIZ ANSWER) THE NORMAL VARIANT IS:

Os supranaviculare.


Using the diagnostic web viewer, we have provided images that assist in telling our clinical story. Areas of significance are indicated below.


FINDINGS: 

Well-corticated triangular-shaped ossicle noted in superior talonavicular articulation with associated underlying osteoedema. No joint effusion or surrounding soft tissue edema evident.

No acute fracture or osteochondral lesion evident.

Tarsal tunnel is unremarkable.

Medial and lateral collateral ligaments are intact.

Flexors and extensors and peroneal tendons and tendon sheaths are unremarkable.

Achilles tendon and plantar fascia are unremarkable.

Patchy areas of scattered osteoedema in keeping with overuse syndrome of young juvenile due to increase bone turnover an reactive hyperemia.


CONCLUSION:

Os supranaviculare. Dorsal fragment is edematous. Spotty marrow edema consistent with overuse syndrome of the young juvenile due to high bone turnover and reactive hyperemia from overuse. In addition, slightly more conspicuous signal in the dysplastic navicular due to overuse syndrome without stress fracture may account for the patient's concentrated medial pain syndrome.


ADDITIONAL EDUCATIONAL NOTES:

What is the main abnormality?

On the Sagittal T1 and T2 Fat Sat FSE images, there are innumerable patchy foci of T1 hypointense and T2 hyperintense marrow signal involving the subcortical bone and scattered within the medullary cavity of all of the tarsal bones and distal tibia. 

These patchy marrow changes are often seen in the feet of asymptomatic active children, postulated to represent residual red marrow or physiologic stress from increased bone remodeling, as they are absent in children after 15 years of age. 

In this patient of this age and with this clinical history, the appearance is most compatible with overuse syndrome of the young juvenile due to high bone turnover and reactive hyperemia from overuse.


What are the imaging differentials for marrow edema in the juvenile?

Main imaging differential diagnosis to consider in this case is chronic regional pain syndrome which is often indistinguishable on MR imaging from overuse syndrome or altered biomechanics. Clinical correlation with pilomotor signs is crucial in the diagnosis of complex regional pain syndrome (CRPS). In this case, there was no history of pilomotor signs or symptoms.

CRPS affects children 5-17 years of age and has a predilection for adolescent girls. Fracture is the most common inciting event, accounting for up to 40% of cases, followed by blunt trauma and surgery. This patient also has no such clinical history of an inciting event to suggest chronic regional pain syndrome.

Other marrow edema or marrow replacing conditions to consider in a paediatric patient are as follows, however, they do not apply to this case as the pattern of marrow involvement is rather different (please review the RadioGraphics article as referenced below).

-Marrow infiltration from neoplastic process such as ALL or lymphoma or metastasis

-Trauma with microtrabecular stress fracture / injury

-Infection

-Juvenile inflammatory arthritis


Can you spot the normal variant?

There is a small well corticated triangular-shaped ossicle noted in the superior talonavicular articulation with associated underlying osteoedema. Given the typical location and corticated margins, it is an os supranaviculare, not to be mistaken for a fracture fragment. 

In this case, there is slightly more conspicuous signal in the dysplastic navicula due to overuse syndrome which may account for the patient’s concentrated medial pain syndrome.


Reference

Chan, B.Y., et al., "MR Imaging of Pediatric Bone Marrow", RadioGraphics, Vol.36, No.6, 2016.

Discussion
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