A congenital digit-like bone located posterior to the cervical spine, occasionally termed the cervical digit, is an extremely rare anomaly ^{[1,2,3,4,5,6]}. Nakano et al. reported the imaging findings of a female infant with a cervical digit, which were accompanied by abnormal segmentation of the adjoining neural arches ^[1]. She underwent three-dimensional computed tomography (3D-CT) at the ages of 3 and 7 years, which revealed morphological changes in the malformation over time. This report describes the age-related atypical evolution of this structure using imaging techniques.

The girl was born with a hard projection from the posterior neck. A 3D-CT revealed a digit-like structure attached to the lamina of C5, associated with malsegmentation of the right posterior arches of C4-C5-C6 (hypoplasia of C4 and fusion between C5 and C6) ^[1]. She was asymptomatic during infancy and early childhood. At 3 years of age, restriction of neck movement was noted, which progressed slowly thereafter. Neurological examination remained normal; she had no pain, and management consisted of clinical and radiological follow-up without surgery. A 3D-CT performed at 3 and 7 years of age revealed progressive ankylosis of the bilateral posterior arches of C4, C5, and C6, complete ankylosis on the right side, and incomplete fusion on the left side. Digit-like bone projections coalesced with the posterior neural arch of C5 and appeared as spinous process-like bulky bone projections (Figs. 1 and 2). Axial computed tomography images taken at 7 years of age excluded spinal canal stenosis at poorly segmented levels (Fig. 3).

Figure 1: The three-dimensional computed tomography performed at the age of 3 years reveals progressive fusion in the posterior arches of vertebrae at C4–6 levels, together with deformed digit-like bone.

Figure 2: The three-dimensional computed tomography, performed at the age of 7 years, reveals overt ankylosis of the posterior arches of C4, C5, and C6, and the cervical digit evolves into a bulky bone projection contiguous with the right posterior arch of C4 and C5, mimicking a spinous process.

Figure 3: Axial view of the computed tomography, performed at the age of 7 years, indicates that the spinal canal is normal.

The progression observed in this case, from a congenital digit-like bone attached to the cervical vertebrae to a hyperplastic spinous bone, differs from what is seen in most cases of cervical digits. In these cases, the condition typically manifests as supernumerary digit- or phalanx-like bone(s) that retain their morphological characteristics from birth to adulthood ^[2,3,4,5,6]. In contrast, the final manifestations observed in our patient resembled those found in patients with an anomalous spinous process or a posterior neural arch ^{[7,8,9,10,11]}. As observed in the present case, although an anomalous or hyperplastic projection from the spinous process or neural arch is not completely ossified, bone protrusion may be confused with a typical cervical digit (a supernumerary bone posterior to the cervical spine). Thus, we would like to term such cases with a malformed projection of the neural arch “atypical cervical digit”. Table 1 summarises previous reports on typical and atypical cervical digits.

Table 1: Case reports of cervical digit

The association with ankylosis or malsegmentation of the posterior neural arches observed in the present case may be unique compared to the manifestation of atypical cases with cervical digits. Most cases of atypical cervical digits show only morphological aberrations of the posterior neural arch. There was only one documented case of an atypical cervical digit associated with spinal malsegmentation; however, a 9-year-old boy showed an elongated spinous process of C5, accompanied by a hemivertebra of C4 in a previous report ^[7]. In the present case, malsegmentation of the anterior spinal component differed from that of the posterior neural arch. From a developmental perspective, the present case is classified under the broad category of Klippel–Feil syndrome, which is characterised by congenital fusion of two or more cervical vertebrae ^[12,13].

The present case represents a rare congenital anomaly characterised by a digit-like bone arising from the cervical spine and progressive hyperplasia of the posterior neural arch. This uncommon association can manifest as atypical cervical digits. It is tempting to consider the cervical digit as a heterogeneous group of anomalies, with malsegmentation of the cervical spine being one subgroup within this category.

A cervical digit as a congenital anomaly may change with ageing, such as atypical evolution of its structure and progressive cervical malsegmentation.