An 11-year-old boy with known postaxial polydactyly in the context of an Ellis-van Creveld syndrome (EvC) consulted for a posttraumatic control. Besides the evaluation of the radial fracture, a radiological and MR analysis of the asymptomatic postaxial polydactyly type A was performed.
The patient was previously diagnosed as EvC with a rare type of polycarpyly (DOI: 10.1594/EURORAD/CASE.12659)
The radiography revealed a postaxial polydactyly with partial proximal synmetacarpalism V-VI. The 6th digit had only two phalanges (hypertrophic proximal and a distal). There was a fifth distal carpal bone (FDCB) at the ulnar side, articulating with the synmetacarpal. There was a right-left symmetry.
MRI moreover showed the more dorsal position of the distal 5th metacarpal. The tendon of the m. extensor digiti minimi (EDM) was running distally to the 5th finger, as the superficial and deep long flexor tendons. Although the hypothenar muscles were more centred around the 6th metacarpal, the tendons of the m. flexor (FDM) and m. opponens digiti minimi (ODM) were located at the 5th finger. Only the tendon of the m. abductor digiti minimi (AbDM) ran to the 6th finger. No large flexor tendons ran to the 6th finger.
The Ellis-van Creveld Syndrome (EvC) (chondroectodermal dysplasia, six-fingered dwarfism) is a very rare genetic disorder of the skeletal dysplasia type, classified as a type of mesomelic limb shortening in the group of the short rib-polydactyly dysplasias (OMIM #225500). The reported incidence is in 1/1.500.000 births with an equal sex ratio. EvC is caused by loss-of-function mutations in the genes EVC or EVC2, the phenotype associated with the mutations in these genes being indistinguishable. The inheritance pattern is autosomal recessive.
Bilateral postaxial polydactyly is a constant finding. There are two types, a type A (well-formed digit) and a type B (rudimentary skin tag, designated as vestigial digit). Five subtypes are identified in type A [1]. One or more accessory carpal bones may be noticed, mostly on the ulnar side of the hamate bone (the so-called FDCB) [2, 3]. The FDCB is a remnant of more primitive tetrapod mammals [2]. The abnormalities tend to be symmetrical [3].
MRI showed, as well as plain radiography but without the use of ionizing radiation, a postaxial hexadactyly [4]. As usual, there was a partial segmentation of the 5th and 6th metacarpal and the extra digit had only two phalanges (hypertrophic proximal and distal). When the FDCB—as in our case—is not fused with the hamate bone, it articulates with the bases of the 5th and/or 6th metacarpals distally. MRI moreover showed that the EDM tendon was running distally adjacent to the 5th finger, as did the superficial and deep long flexor tendons. The tendons of the FDM and ODM ran adjacent to the 5th finger, whereas the tendon of the AbDM was located adjacent to the 6th finger. Also the more dorsal position of the 5th metacarpal is demonstrated clearly. Axial T1-SE and coronal T1-SE and T2-FS sequences are mandatory. In patients experiencing painful motion, more sensitive STIR sequences may be added - only for diagnostic reasons - in order to demonstrate dysfunctional bone marrow oedema due to the defective bony configuration. The longer examination time of MRI (versus plain radiography) poses no problem for the normal intelligent EVC patient.
When reconstruction of a type A is considered (not functional digit or for cosmetic reasons) MRI may precise pre-operative anatomy to plan the section planes and allow maximal preservation of the present muscle(s).
As far as we could establish, no previous MR studies of the hand or wrist in EVC have been published.
MR findings of postaxial polydactyly type A in EvC
The patient is an 11-year-old male previously diagnosed with Ellis-van Creveld syndrome (EvC), accompanied by postaxial polydactyly. The imaging examinations this time included a wrist X-ray and MRI.
Based on the patient’s known diagnosis and imaging findings, possible or differential diagnoses include:
Considering the patient’s age, previously confirmed diagnosis of Ellis-van Creveld syndrome, typical postaxial polydactyly, and the multi-joint and tendinous structural changes indicated by X-ray and MRI, the most likely diagnosis is:
Ellis-van Creveld syndrome (EvC) with postaxial polydactyly (Type A).
Disclaimer:
The above report is a reference analysis based on current imaging and clinical information and cannot replace in-person consultation or professional medical advice. Specific diagnosis, treatment, and rehabilitation plans should be made after a thorough evaluation of the patient’s actual condition and professional assessments.
MR findings of postaxial polydactyly type A in EvC
