Radiology Teaching Files > Case 796691

Contributed by: John Hunter, Radiologist, University of California, Davis, California, USA.
History: 38 y/o female with right foot pain.

Fig. 1: Axial T1WI through both feet

Fig. 2: Sagittal T1WI through right foot
Diagnosis: Bilateral accessory navicular bones (Type II AN).

See also Case 30c

There are two types of AN. Type I AN (30%) represents a sesamoid bone in the posterior tibialis tendon at the insertion into the navicular. They tend to be round or oval and may be seen up to 5mm medial and posterior to the medial aspect of the navicular. Some feel that the Type I AN leads to flat foot deformity secondary to altered biomechanics and failure of the posterior tibial tendon.

Type II AN (70%) represents an accessory ossification in the tubercle of the navicular. These are often triangular or heart shaped, usually within 1-2 mm of the medial and posterior aspect of the navicular bone. These are usually the ones that are symptomatic with local pain and tenderness.

In this case, the flattened distal margin of the AN and its proximity to the navicular suggest a Type II lesion, with some mild increased signal intensity on the FSE images.


Source: John Hunter's MSK Teaching File: Misc. MRI Case 99

REF.: Resnick, Bone and Joint Imaging. WB Saunders, 1989. P.1073.

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Additional Details:

Case Number: 796691Last Updated: 10-21-2004
Anatomy: Skeletal System   Pathology: Other
Modality: MRExam Date: Access Level: Readable by all users

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