We report the case of a child with genetically confirmed tetrasomy 18p and nonspecific neuroimaging findings that may mimic acquired white matter injury or imaging patterns associated with cerebral palsy. This case report was approved by the Institutional Review Board of Keimyung University Dongsan Hospital (IRB No. 2026-02-015), which waived the requirement for informed consent.

A male child was referred for evaluation of global developmental delay and hypotonia. He had been born at term without perinatal complications. Developmental milestones were delayed, and generalized hypotonia was noted during infancy. Neurological examination revealed generalized axial and appendicular hypotonia, with no persistent extremity hypertonia, spasticity, asymmetric tone abnormality, or pyramidal signs.

Conventional cytogenetic analysis using G-banding demonstrated a supernumerary isochromosome derived from the short arm of chromosome 18, resulting in a karyotype of 47,XY,+i(18)(p10) (Fig. 1A). Chromosomal microarray analysis using the CytoScan™ DX Assay (Thermo Fisher Scientific, Waltham, MA, USA) further identified a four-copy gain spanning 18p11.32–18q11.1 (chr18:136,226–18,521,285; GRCh37/hg19), encompassing the entire short arm of chromosome 18 and the proximal 18q11.1 region, consistent with tetrasomy 18p (Fig. 1B). Parental karyotyping was unavailable; therefore, a de novo origin could not be definitively established. Because most tetrasomy 18p cases reported in the literature arise de novo, and because neither parent showed clinical features suggestive of the condition, a de novo mechanism was considered likely in the present case, although it remains unconfirmed [1-3].

Brain magnetic resonance imaging (MRI) demonstrated thinning of the distal body of the corpus callosum, diffuse prominence of the cortical sulci consistent with cortical volume loss, and reduced periventricular white matter volume with mild ventricular prominence (Fig. 2). The term ‘periventricular leukomalacia (PVL)-like’ was used descriptively to indicate the periventricular distribution of the white matter signal abnormality and volume reduction. However, because the patient had no history of prematurity, perinatal hypoxic–ischemic injury, or neonatal neurological events, these findings were interpreted as nonspecific white matter underdevelopment rather than definite acquired PVL.

Although neurological manifestations are common in tetrasomy 18p, brain MRI findings have been described infrequently, and most reports have focused on clinical and cytogenetic features rather than detailed neuroimaging characterization [1,2,4]. Neuroimaging findings in chromosome 18 disorders are heterogeneous and vary according to the chromosomal region involved. In particular, imaging patterns reported in 18q-related abnormalities, such as those described by Malik et al. [5], should not be directly extrapolated to tetrasomy 18p, which results from an isochromosome 18p and copy-number gain of the short arm of chromosome 18.

Among reported cases of tetrasomy 18p with neuroimaging data, Sebold et al. [1] noted brain abnormalities in a subset of their 43-patient cohort but did not provide systematic MRI characterization. Bawazeer et al. [2] and He et al. [4] each described a single case with limited neuroimaging detail. Lim et al. [6] reported a pediatric case that presented as spastic cerebral palsy with PVL-like white matter changes and corpus callosum involvement. These findings closely overlap with those in the present case and underscore the risk of misdiagnosis when genetic evaluation is deferred.

These MRI findings are not specific to tetrasomy 18p and may overlap with those of several pediatric neurological conditions, including acquired PVL, cerebral palsy related to perinatal injury, congenital brain malformations, and metabolic or neurodegenerative disorders. In the present case, the key discriminating factors were the absence of prematurity or documented perinatal hypoxic–ischemic injury, which made an acquired etiology insufficient to fully explain the neuroimaging findings, together with global developmental delay, generalized hypotonia, and dysmorphic features, which raised suspicion for a chromosomal disorder. This constellation of findings prompted chromosomal microarray analysis, which established the definitive diagnosis.

The present case does not establish a disease-specific MRI pattern for tetrasomy 18p. Rather, its significance lies in showing that a combination of nonspecific MRI abnormalities—corpus callosum thinning, cortical volume loss, and reduced periventricular white matter volume—may resemble acquired white matter injury or cerebral palsy-like clinical presentations. The case also highlights that precise genetic characterization, including chromosomal microarray analysis, is essential for accurate diagnosis in children who present with developmental delay and tone abnormalities in the absence of sufficient perinatal risk factors.