DOI: 10.1148/radiol.2452050010
(Radiology 2007;245:604-605.)
© RSNA, 2007
The Anteater Nose Sign1
Vernon M. Chapman, MD
1 From the Department of Radiology, Massachusetts General Hospital, 55 Fruit St, FND 216, PO Box 9657, Boston, MA 02114. Received January 4, 2005; revision requested February 3; revision received February 14; final version accepted April 14.
Address correspondence to the author (e-mail: vernon.chapman{at}riaco.com).
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APPEARANCE
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The anteater nose sign is caused by a tubular elongation of the anterior process of the calcaneus that approaches or overlaps the navicular bone and resembles the nose of an anteater (Figure) on a lateral foot or ankle radiograph (1).
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Lateral radiograph of the foot demonstrates anteater nose sign, which is caused by abnormal tubular elongation (arrows) of the anterior process of the calcaneus with overlap of the navicular bone.
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EXPLANATION
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This sign is seen in patients with calcaneonavicular tarsal coalition and a calcaneonavicular bar (the anteater nose), which is an osseous bar or anomalous articulation between the anterior process of the calcaneus and the navicular bone.
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DISCUSSION
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Tarsal coalition is a congenital malformation of the foot, thought to be the result of embryonic failure of tarsal segmentation and resulting in abnormal osseous, cartilaginous, or fibrous communication between bones within the hindfoot or midfoot or between bones of the two areas. Prevalence is estimated at 1%–2% of the population (2,3); however, it may be higher, because many patients are asymptomatic. Tarsal coalition is inherited as an isolated autosomal dominant trait with variable penetrance and may occur in association with other anomalies (4). Bilateral coalitions are seen in 40%–68% of affected patients (3). Symptomatic patients usually present in late childhood or adolescence with restricted subtalar movement and painful, rigid, flatfoot deformity with contracture of the peroneal tendons (peroneal spastic flatfoot).
The most common of these tarsal conditions is calcaneonavicular coalition, followed by middle facet talocalcaneal coalition (5). Patients with calcaneonavicular coalition typically become symptomatic between 8 and 12 years of age, when the cartilaginous calcaneonavicular bar undergoes ossification. This coalition is best demonstrated on a 45° internal oblique radiograph of the foot. Secondary signs are present on the lateral foot or ankle radiograph, including the anteater nose sign and hypoplasia of the talus (6,7). Computed tomography and magnetic resonance imaging are generally not necessary to make the diagnosis of calcaneonavicular coalition, however they may be useful for excluding a coexistent talocalcaneal coalition, which is difficult to diagnose on radiographs (8–10).
Treatment of symptomatic calcaneonavicular coalition without tarsal joint degenerative change often requires surgical excision of the calcaneonavicular bar, with interposition of the extensor digitorum brevis muscle (11). Between 77% and 90% of patients have good or excellent results, with treatment failures attributed to talonavicular or subtalar joint arthritis, incomplete excision, or recurrence of the coalition (12). Patients with tarsal joint degenerative change are best treated with triple arthrodesis (13).
In conclusion, calcaneonavicular tarsal coalition is a cause of foot pain and deformity that can be identified on a lateral radiograph of the foot or ankle on the basis of the presence of the anteater nose sign.
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FOOTNOTES
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Author stated no financial relationship to disclose.
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References
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- Harris RI, Beath T. Etiology of peroneal spastic flatfoot. J Bone Joint Surg Br 1948;30:624–634.
- Cooperman DR, Janke BE, Gilmore A, Latimer BM, Brinker MR, Thompson GH. A three-dimensional study of calcaneonavicular tarsal coalitions. J Pediatr Orthop 2001;21(5):648–651.[CrossRef][Medline]
- Wray JB, Herndon CN. Hereditary transmission of congenital coalition of the calcaneus to the navicular. J Bone Joint Surg Am 1963;45:365–372.[Abstract/Free Full Text]
- Stormont DM, Peterson HA. The relative incidence of tarsal coalitions. Clin Orthop Relat Res 1983;181:28–36.[Medline]
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- Gonzalez P, Kumar SJ. Calcaneonavicular coalition treated by resection and interposition of the extensor digitorum brevis muscle. J Bone Joint Surg Am 1990;72:71–77.[Abstract/Free Full Text]
- Moyes ST, Crawfurd EK, Aichroth PM. The interposition of extensor digitorum brevis in the resection of calcaneonavicular bars. J Pediatr Orthop 1994;14:387–388.[Medline]
- Swiontkowski MF, Scranton PE, Hansen S. Tarsal coalitions: long-term results of surgical treatment. J Pediatr Orthop 1983;3:287–292.[Medline]
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