Why this case matters

Joubert syndrome (JS) is a rare inherited condition that affects early brain development and can involve other organs, including the eyes and liver. For families, the diagnosis often begins with questions about developmental differences, feeding or growth concerns, vision changes, and what testing may be needed next. A 2026 case report in Radiology Case Reports adds to the evidence that brain imaging in JS should look beyond its best-known hallmark—the “molar tooth sign”—to assess other brain structures and possible multisystem involvement.

The report describes a 4-month-old boy with developmental delay and progressive weight loss. Magnetic resonance imaging (MRI) showed features diagnostic of JS as well as hippocampal malrotation, an unusual shape and position of a structure deep within the brain. The infant also had retinal degeneration and elevated liver enzymes. Together, these findings illustrate the broad range of tissues that can be affected in a ciliopathy, a group of genetic disorders caused by changes in the function of cellular structures called cilia.

The molar tooth sign: the central imaging clue

JS is defined by a characteristic pattern on brain MRI called the molar tooth sign. On certain MRI views, the midbrain region resembles the cross-section of a molar tooth. This appearance reflects three related developmental changes:

  • Underdevelopment of the cerebellar vermis, the central portion of the cerebellum that helps coordinate movement and balance
  • Superior cerebellar peduncles that are thicker and oriented more horizontally than usual
  • A deeper-than-usual space between parts of the midbrain, called the interpeduncular fossa

In this infant, MRI identified the molar tooth sign and vermian hypoplasia, supporting the diagnosis of Joubert syndrome. Recognizing this imaging pattern is important because it connects neurologic findings with the possibility of eye, liver, kidney, and other organ involvement within the JS spectrum.

A closer look at hippocampal malrotation

The particularly notable feature in this report was hippocampal malrotation. The hippocampus is a structure involved in memory and is located in the temporal lobe of the brain. During typical development, it takes on a characteristic curved shape. In hippocampal malrotation, its shape and orientation differ from what is usually seen.

Hippocampal malrotation is considered a supratentorial finding—meaning it occurs in the portion of the brain above the cerebellum and brainstem. By contrast, the molar tooth sign involves the midbrain and hindbrain. Although hippocampal malrotation has previously been described in JS and related disorders, it is less widely recognized than the molar tooth sign.

Its clinical importance remains uncertain. In particular, the report notes that it is not yet clear whether hippocampal malrotation is linked to epilepsy in people with JS. This uncertainty is meaningful: an imaging finding may be relevant to brain development without necessarily predicting seizures, developmental outcomes, or a specific future complication. More cases and larger studies will be needed to understand whether this feature has consistent clinical implications.

Signs of a multisystem ciliopathy

The child in this report also had retinal degeneration and elevated transaminases, which are liver enzymes measured in blood tests. These findings raise concern for involvement beyond the brain.

Retinal degeneration can affect vision because the retina is the light-sensitive tissue at the back of the eye. Its presence in a child with JS reinforces the importance of evaluating visual function and monitoring eye health as part of a broader assessment. Elevated transaminases may point to liver involvement, another recognized concern within the Joubert ciliopathy spectrum.

The combination of developmental delay, brain MRI findings, retinal degeneration, and abnormal liver enzymes demonstrates why JS care often requires a coordinated approach. The case does not establish how often these features occur together, but it shows how information from imaging, eye assessment, and laboratory testing can contribute to a more complete clinical picture.

What this means for treatment and care

This report does not test a new treatment. Its main practical message is about assessment: clinicians evaluating a child with suspected or confirmed JS may benefit from carefully examining both the hindbrain and the upper parts of the brain on MRI, while also considering evaluation for effects outside the nervous system.

For patients and families, identifying the full pattern of involvement can help guide individualized care planning. Developmental delay, retinal disease, and potential liver involvement may each require different types of monitoring and support. Importantly, hippocampal malrotation should be viewed as a finding that warrants attention and further study, rather than as a proven predictor of epilepsy or other outcomes.

Building a more complete picture of Joubert syndrome

Single case reports cannot answer every question, but they can highlight patterns that deserve closer investigation. This infant’s imaging findings support growing recognition that JS may include structural differences above the cerebellum as well as the classic molar tooth sign. Future research can clarify how frequently hippocampal malrotation occurs, whether it clusters with particular genetic causes of JS, and whether it is associated with seizures, developmental profiles, or other clinical features.

As imaging techniques, genetic testing, and long-term patient follow-up continue to improve, researchers may be able to map the full neurological and systemic spectrum of Joubert syndrome more precisely. For now, this case offers a valuable reminder: in JS, careful attention to the whole brain—and the whole body—can reveal important information for families and care teams.