IS Case 473: Thrombocytopenia - absent radius syndrome (TAR Syndrome)

Daniel O'Connor, MD

University of Rochester

Imaging Sciences URMC 2010
Publication Date: 2010-08-30


Patient is a 28-year-old male, with congenital abnormalities of the upper extremities bilaterally, who presented to the Emergency Department following trauma to the right wrist and hand from a recent fall.


Standard projections of the right hand and wrist were obtained. The right radius was nearly completely absent with the exception of a small portion of the distal radius, which articulates with a dysmorphic proximal carpal row. The ulnocarpal joint demonstrated some subcondral sclerosis and osteophyte development compatible with accelerated degenerative changes, however, no evidence of acute osseous injury was evident.


Thrombocytopenia - absent radius syndrome (TAR Syndrome)


A number of syndromes feature aplasia or dysplasia of the radius; the radiographic appearance of the affected limb is commonly nonspecific and is unlikely to be diagnostic of the specific syndrome. TAR syndrome is an exception in that the thumb is most often present and normal (or near normal) in size and function; other radial aplasia/dysplasia syndromes are associated with significant deformity (or absence) of the entire radial ray.

Other conditions associated with radial ray dysplasias involving the forearm and/or thumb include Fanconi anemia (absent, dysplastic, or supernumerary thumb; auto recessive; especially among Ashkenazi Jews), Holt-Osram syndrome (absent, dysplastic, or triphalangeal thumb; autosomal dominant), VATER syndrome / VACTERL (limb anomalies may include absent, dysplasic, fused, or supernumerary digits in approximately 70% of affected patients), Trisomy 18, and thalidomide embryopathy, among numerous others.

Although nonspecific, the appearance of radial ray anomalies in an infant should initiate additional investigation into the underlying syndrome. Children born with Fanconi's anemia, for example, are often otherwise healthy with life-threatening anemia not developing until later in childhood. Other than his limb anomalies and low platelet count, our patient was an otherwise healthy individual


  1. Manaster BJ, Roberts CC, Andrews CL, Petersilge CA. Expert Differential Diagnoses: Musculoskeletal. Lippincott Williams Wilkins, 2008.
  2. Dahnert WF. Radiology Review Manual, 6th edition. Lippincott Williams Wilkins, 2007.

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