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Age / Sex : 49 / M
Age / Sex : 49/M
Chief complaint : ankle pain associated
with allegedly known fracture at the syndesmosis and the medial malleolus
1) What is your impression?
Two weeks later, you can see the final diagnosis with a brief discussion of
this case.
* Send Application Answers to In Sook Lee, MD (lis@pusan.ac.kr)
Courtesy : Sungjun Kim, Gangnam Severance Hospital
Diagnosis: Calcaneonavicular coalition
Discussion
Findings: Elongated
anterior process of calcaneus results in peculiar morphology, so called “Anteater
sign”.
Differential Diagnosis: None
Diagnosis:
Calcaneonavicular coalition
Discussion:
Congenital
tarsal coalition likely results from abnormal differentiation and segmentation
of primitive mesenchyme with resultant lack of joint formation. An autosomal
dominant inheritance pattern with variable, if not nearly full penetrance, has
been suggested. The true prevalence of tarsal coalition is not known; estimates
range from far less than 1% of the population to approximately 1%–2%. There is
a probable, slight male predominance, and the condition is bilateral in
approximately 50% of cases.
Approximately 90% of tarsal
coalitions involve the talocalcaneal or calcaneonavicular joints. Although many
investigators believe that calcaneonavicular coalitions are the most commonly
encountered type, others report a nearly equal prevalence of talocalcaneal and
calcaneonavicular coalitions or even a slightly greater prevalence of
talocalcaneal coalitions. Calcaneonavicular coalitions are more readily
diagnosed with conventional radiography, which may contribute to their reported
higher prevalence. Talonavicular coalitions are far less common, and many are
asymptomatic; calcaneocuboid and cubonavicular coalitions are very rare.
Navicular–first cuneiform joint coalitions have also been reported.
Occasionally, multiple coalitions in one foot may be seen.
Calcaneonavicular coalitions are
best depicted on 45° internal oblique radiographs. The calcaneus and navicular
do not normally articulate. With osseous coalition, a bony bar that bridges the
two bones is seen. With fibrous or cartilaginous coalition, the bones are in
close proximity, both have irregular surfaces, and the anteromedial calcaneus
is abnormally widened or flattened. On lateral radiographs, elongation of the
anterior dorsal calcaneus may simulate an anteater's nose. Hypoplasia of the
talus may also be observed with calcaneonavicular coalition.
In
calcaneonavicular coalition, axial CT scans show broadening of the medial
aspect of the anterior and dorsal calcaneus as it lies in apposition to the
navicular. The obliquity of the calcaneonavicular bridging, whether osseous or
nonosseous, makes it difficult to visualize the entire coalition on only one
axial or coronal image. In some cases of nonosseous coalition, changes may be
subtle, with narrowing of the space between the two bones and minimal marginal
reactive bone changes. Cross-sectional imaging is also helpful in the diagnosis
of rare cubonavicular coalition.
Calcaneonavicular coalitions are
best visualized on sagittal and axial MR images. Sagittal images are
particularly valuable because of the orientation of the calcaneonavicular
bridging. The elongated anterior dorsal calcaneus (anteater's nose) may be
visualized on a single image.
References:
Newman JS,
Newberg AH. Congenital Tarsal Coalition: Multimodality Evaluation with Emphasis
on CT and MR Imaging. Radiographics.
2000; 20: 321-332.
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