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PubMed This is a summary of 10 peer-reviewed journal articles Updated
Neurology

Understanding the Brain: Diagnosis and Imaging of Lobar HPE

At a Glance

Lobar holoprosencephaly (HPE) is the mildest classic form of HPE where the brain is mostly separated into two halves. A diagnosis is confirmed by MRI findings like fused frontal horns, an absent cavum septum pellucidum, and typically unfused thalami, indicating better neurological function.

Reading a neuroradiology report for your child can feel like trying to translate a foreign language. However, these reports provide the definitive “map” of your child’s brain and are essential for confirming a diagnosis of Lobar Holoprosencephaly (HPE). Because Lobar HPE is the mildest classic form, the brain will look much more “typical” than in other forms, with separation occurring in most areas except for specific landmarks in the front.

Comparing the Three Classic Forms

To understand why Lobar HPE is considered the mildest form, it helps to see how it compares to the more severe types of HPE [1][2]:

Feature Alobar (Severe) Semilobar (Moderate) Lobar (Mildest)
Brain Separation None; the brain is a single “monoventricle” [3] The back of the brain is separated; the front is fused [1] Most of the brain is separated; fusion is limited to the front [4]
Thalami Always fused (joined) [5] Usually partially fused [6] Typically unfused (separate) [4]
Middle “Split” Completely missing [6] Present only in the back half [1] Mostly complete along the midline [4]

Key MRI Findings in Lobar HPE

For a doctor to confirm a diagnosis of Lobar HPE, specific anatomical features must be present on an MRI (Magnetic Resonance Imaging) scan [7]. The following are the most critical “landmarks” doctors look for:

  • Fused Frontal Horns: The lateral ventricles are fluid-filled chambers in the brain. In a typical brain, they have two separate “horns” in the front. In Lobar HPE, these two horns are joined together across the middle [7][6].
  • Absent Cavum Septum Pellucidum (CSP): The CSP is a tiny, fluid-filled space that normally sits between the two frontal horns. Its absence is a hallmark sign that the brain did not fully separate in that area [7][8].
  • Interhemispheric Fissure: This is the deep “valley” or groove that separates the left and right halves of the brain. In the Lobar form, this groove is present almost everywhere, though it may be shallow or missing at the very front [4].
  • Unfused Thalami: The thalami are two egg-shaped structures that act as the brain’s relay stations. In Lobar HPE, these are almost always two separate structures, which is a very positive sign for neurological function [4][7].

Decoding Your Child’s Radiology Report

You may see the following terms on your child’s medical reports. Here is what they mean in plain English:

  • Hypoplasia of the Corpus Callosum: The “bridge” of nerves that allows the two sides of the brain to talk to each other is thinner than normal or missing some parts [9][6].
  • Cortical Dysplasia / Heterotopia: These terms mean that some of the brain’s “gray matter” (the cells that do the thinking) ended up in the wrong spot during development [9][10].
  • Coronal View: This refers to a “head-on” view of the brain (like looking at a face), which is the best angle for seeing the fusion of the frontal horns [7].

Diagnosis Checklist

When reviewing your child’s imaging results with a neurologist, you can use this checklist to ensure all key areas have been evaluated:

  1. Is the interhemispheric fissure present for most of the brain’s length? [4]
  2. Are the thalami separate (unfused)? [4]
  3. Are the frontal horns of the ventricles joined/fused? [7]
  4. Is the cavum septum pellucidum absent? [7]
  5. Is the corpus callosum present, and if so, is it fully formed? [9]

Common questions in this guide

What makes Lobar HPE different from other forms of holoprosencephaly?
Lobar HPE is considered the mildest classic form. Unlike severe forms where the brain is a single structure, most of the brain is separated into two halves in Lobar HPE, with fusion usually limited only to specific areas in the front of the brain.
What does it mean if my child's MRI shows fused frontal horns?
Fused frontal horns mean that the two fluid-filled chambers in the front of the brain are joined together across the middle. This is a key anatomical hallmark that doctors look for on an MRI scan to confirm a diagnosis of Lobar HPE.
Are the thalami fused in Lobar HPE?
In Lobar HPE, the thalami are typically completely separate, or unfused. This is a very positive sign for your child's neurological function and helps doctors distinguish this condition from more severe forms of holoprosencephaly.
What is hypoplasia of the corpus callosum?
Hypoplasia means the corpus callosum, which is the crucial nerve bridge connecting the left and right sides of the brain, is thinner than normal or missing some parts. This is a very common finding on radiology reports for children with Lobar HPE.
Why do doctors check for the cavum septum pellucidum (CSP)?
The CSP is a tiny fluid-filled space that normally sits between the frontal horns of the brain. Its absence on a child's MRI scan is a major indicator that the brain did not fully separate in that specific area during prenatal development.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Can you point out the fused frontal horns on my child's MRI scan and show me how they differ from a typical scan?
  2. 2.Is the interhemispheric fissure present throughout the entire brain, or are there areas in the front where it disappears?
  3. 3.Are the thalami completely separate, or is there any sign of partial fusion in that region?
  4. 4.Did the radiologist notice any other findings, such as 'heterotopia' or 'cortical dysplasia,' that might affect my child's development?
  5. 5.Is the corpus callosum (the bridge between the two sides) fully formed, or is it 'hypoplastic' (smaller than usual)?

Questions For You

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References

References (10)
  1. 1

    Alobar Holoprosencephaly in a Newborn: A Case Report of Prenatal Diagnosis and a Review of the Literature.

    Chafiq K, Toumi K, Khayi FE, Daoudi A

    Cureus 2024; (16(11)):e74462 doi:10.7759/cureus.74462.

    PMID: 39726469
  2. 2

    Semilobar Holoprosencephaly: Capacious Anomaly in the Cephalad.

    Veluchamy M, Murugan M

    Cureus 2020; (12(7)):e9181 doi:10.7759/cureus.9181.

    PMID: 32802616
  3. 3

    Neuropathology of holoprosencephaly.

    Fallet-Bianco C

    American journal of medical genetics. Part C, Seminars in medical genetics 2018; (178(2)):214-228 doi:10.1002/ajmg.c.31623.

    PMID: 30182440
  4. 4

    Lobar holoprosencephaly with associated meningocele: A rare case report of a 25-year-old patient with multiple seizures.

    Barman P, Mishra GV, Murugan G, et al.

    Radiology case reports 2025; (20(4)):2004-2008 doi:10.1016/j.radcr.2025.01.029.

    PMID: 39963386
  5. 5

    Aventriculi associated with holoprosencephaly in a dog.

    Barnard L, Durand A, Blume L, et al.

    Journal of veterinary internal medicine 2020; (34(6)):2682-2686 doi:10.1111/jvim.15907.

    PMID: 33009835
  6. 6

    Lobar holoprosencephaly with craniofacial defects in a Friesian calf: A case report.

    Kisipan ML, Nyaga SN, Thuo JN, et al.

    Veterinary medicine and science 2020; (6(3)):454-461 doi:10.1002/vms3.244.

    PMID: 31972069
  7. 7

    Cyclopia: Facial deformity indicating severe holoprosencephaly with imaging findings of brain: A case report.

    Aryal S, Rimal B, Paudel S, Marasini K

    Radiology case reports 2026; (21(4)):1706-1711 doi:10.1016/j.radcr.2025.12.059.

    PMID: 41727820
  8. 8

    The wide spectrum of ultrasound diagnosis of holoprosencephaly.

    Ionescu CA, Vladareanu S, Tudorache S, et al.

    Medical ultrasonography 2019; (21(2)):163-169 doi:10.11152/mu-1614.

    PMID: 31063520
  9. 9

    Congenital external hydrocephalus: A rare presentation of lobar holoprosencephaly in a neonate.

    Agrawal R, Raj N, Dhawan V, et al.

    Radiology case reports 2025; (20(5)):2323-2327 doi:10.1016/j.radcr.2025.01.080.

    PMID: 40129779
  10. 10

    Subcortical heterotopia appearing as huge midline mass in the newborn brain.

    Fukumura S, Watanabe T, Kimura S, et al.

    Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2016; (32(2)):377-80 doi:10.1007/s00381-015-2841-0.

    PMID: 26231566

This page explains Lobar HPE MRI terminology for educational purposes. Always rely on your child's pediatric neurologist or neuroradiologist to interpret their specific imaging reports and determine their care plan.

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