Is It or Isn’t It Abnormal in This Classification System?

Patient Presentation
A 6-year-old male came to clinic for a second opinion regarding the results of a head computed tomography study. Two weeks previously, the patient had fallen off from a slide onto hard ground. He had loss of consciousness for at least 1 minute and had been awake but very groggy in the emergency room. He had emesis three times so head imaging was done. It was negative for any acute bleeding or obvious injury, but it was noted that his cerebellar tonsils were 4 mm below the foramen magnum and there was concern for a Chiari I malformation. The patient had recovered without incident but his local nurse practitioner was unsure what to do about these incidental findings so she referred him for the second opinion. The past medical history was non-contributory. The family history was positive for migraine in the maternal family and a paternal second cousin with a neurological genetic disease of unknown type. The review of systems was normal and he had no headaches, balance or muscle problems.

The pertinent physical exam showed a smiling boy with growth parameters in the 50-75% and normal vital signs. HEENT was normal including pupils. His skin examination showed a few freckles on arms and face. Neurological examination was normal including gait and fine motor activities. His spine had no identifiable defects and he appeared to have full range of motion in his joints including his neck.

The diagnosis of of a healthy boy who had recovered from his head trauma was made. The pediatrician was able to determine that the cerebellar tonsils should be 3 mm or less to be considered normal and 5 mm or more to be considered abnormal for a Chiari I malformation. The pediatrician noted that the child had been perfectly well before this and probably would continue to be. However, it was possible that this should be followed at intervals and neurosurgery usually followed or treated these patients. The parents expressed that they also were very anxious about this and wanted to talk more with a specialist. Therefore the patient was referred and the neurosurgeon felt that this was a normal variant which did not need specific followup. He did caution that if the patient did develop any more consistent or increasing neurological problems that consultation should be sought just like any patient without this finding.

Chiari I malformations have caudal displacement of cerebellar tonsils with elongation of the 4th ventricle. It is associated with syringomyelia in up to 80% of patients. Syringomyelia is a cyst-like formation within the spinal cord that contains altered glial elements. This may be asymptomatic or have symptoms occurring from infancy to adulthood. Most patients present in the 3rd decade. Hydrocephalus may be present. A review can be found here.

Classifying information and diseases is important in clinical care as it can help determine treatment and prognosis, and improves communication among clinicians and facilitates research.

There are 5 ways to organize and classify information, sometimes referred to as LATCH. These types are often used together sequentially. For example, restaurants in particular city (location), then by cuisine type (category) and then name (alphabetical).

  • Location – this commonly uses a visual representation of a physical space such as a map. In medicine, anatomic location is very important especially in the surgical, radiology, and oncology specialties.
  • Alphabetical – this is helpful when the terms and definitions are already known by people. It can be less helpful if people are not aware. It is very good for lists or as a secondary method of information organization.
  • Time – chronological organization is used for events. In medicine this a major organizer of the medical chart. Age of the patient is also important for developing a differential diagnosis especially in pediatrics. It is also helpful for understanding processes such as quality improvement.
  • Category – this is probably the broadest way to organize information. Medical specialties and patient problems lists are organized this way.
  • Hierarchy – this method shows how information is related to each other and potentially may indicate importance or rank. For example, pediatrics – pediatric neurology – muscle diseases – spinal muscle atrophy.

Learning Point
Disease classification systems help to define the problem. They allow everyone to understand and use the definitions more consistently. If people all agree on the terminology, it makes mis-understandings less likely. This is important in clinical care but is also especially important in quality improvement and research where treatments and outcomes must be clearly understood based on a very specific type of problem.

Take, for example, growth plate fractures. The Salter-Harris classification system uses an anatomical approach to define 5 different growth plate fractures. Using this location categorization, the radiologist and orthopaedic surgeon can quickly have a shared understanding of the fracture type, and treatment decisions and natural history will be made and based on the classification, as type 1 fractures are treated conservatively and have generally good outcomes, and types 4 and 5 are treated surgically and have poorer expected outcomes.

Some classification schemes are objective in that they discriminate between each class, but are qualitative as it is up to the clinician to determine the classification. This can be more difficult when a clinician is trying to assign a discrete classification to something that is a continuous process such as Tanner staging for pubertal development. With Tanner staging there are 5 distinct stages, however as puberty is a continuum, patients still must cross the line between the stages and therefore clinicians will often record Tanner II-III or IV-V in their chart. Another example is the Bristol Stool Scale for fecal stool classification. This is a visual tool of 7 different stool types and patients often indicate several of the classifications to describe even their “normal” stool pattern. Another example is the Mallampati airway visualization score which can be impeded by patient cooperation with the examination and therefore the classification may not be as accurate as one tries to make it. These types of classification schemes are very important to help guide evaluation, management and treatment but many times in clinical care are used less rigidly, i.e. it is more important to know the patient generally has harder or softer stools than the exact 1-7 category.

Classification schemes using measurements can potentially be more reproducible, precise and accurate. Examples would be measurements of a skin macule, radiographic measurements (i.e. organ or mass size), and surgical specimens. These are continuous variables where often someone is looking to determine a specific size or “cut-off” where it is more likely to indicate a more serious problem. For example, the thickness of the pylorus in a newborn is considered normal up to 3.5 mm. If it larger then pyloric stenosis is more likely in the setting of a frequently vomiting neonate. Cancer classification schemes use size as an important characteristic and look for changes in size to help determine response to treatment as well. There often is a grey zone too between what may be clearly normal and what is diseased and patients will fall into these areas too.

There are other classification schema which are more difficult to apply even when they are well-established and understood. A common pediatric example is otitis media. Clinicians know that otitis media with suppurative effusion should be distinguished from otitis media with serous effusion as it is one of the key characteristics that helps determine if antibiotics are indicated. However patient cooperation, crying, temperature, and especially cerumen make it very difficult to examine the middle ear and determine if an effusion is present and what type of effusion it is.

Sometimes there are more than one classification system for different medical problems, which can be caused by different or disputed terminology, and evolving scientific understanding of disease processes. Classification of cancers is a classic example. Therefore it can be very important to understand which classification system is being used.

Questions for Further Discussion
1. List some other common classification systems that you use frequently?
2. What are indications for head imaging after head injury?
3. What are indications for a neurosurgery consultaton?
4. What are some ways that “cut-off” values are determined?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Chiari Malformation

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Chatrath A, Marino A, Taylor D, Elsarrag M, Soldozy S, Jane JA Jr. Chiari I malformation in children-the natural history. Childs Nerv Syst. 2019 Oct;35(10):1793-1799. doi: 10.1007/s00381-019-04310-0.

Talamonti G, Marcati E, Gribaudi G, Picano M, D’Aliberti G. Acute presentation of Chiari 1 malformation in children. Childs Nerv Syst. 2020 May;36(5):899-909. doi: 10.1007/s00381-020-04540-7.

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa