2024 ICD-10-CM Diagnosis Code G91.9

Hydrocephalus, unspecified

ICD-10-CM Code:
ICD-10 Code for:
Hydrocephalus, unspecified
Is Billable?
Yes - Valid for Submission
Chronic Condition Indicator: [1]
Code Navigator:

Code Classification

  • Diseases of the nervous system
    • Other disorders of the nervous system
      • Hydrocephalus

G91.9 is a billable diagnosis code used to specify a medical diagnosis of hydrocephalus, unspecified. The code is valid during the current fiscal year for the submission of HIPAA-covered transactions from October 01, 2023 through September 30, 2024.

Unspecified diagnosis codes like G91.9 are acceptable when clinical information is unknown or not available about a particular condition. Although a more specific code is preferable, unspecified codes should be used when such codes most accurately reflect what is known about a patient's condition. Specific diagnosis codes should not be used if not supported by the patient's medical record.

Approximate Synonyms

The following clinical terms are approximate synonyms or lay terms that might be used to identify the correct diagnosis code:

  • Acquired hydrocephalus
  • Acquired hydrocephalus of newborn
  • Aqueduct of Sylvius anomaly
  • Arrested hydrocephalus
  • Cerebrospinal fluid rhinorrhea
  • Cerebrospinal fluid rhinorrhea due to hydrocephalus
  • Cranial cerebrospinal fluid leak
  • External hydrocephalus
  • Hydrocephalus
  • Hydrocephalus with anomaly of aqueduct of Sylvius
  • Internal hydrocephalus
  • Leak of cranial cerebrospinal fluid due to hydrocephalus

Clinical Classification

Clinical Information

  • Dandy-Walker Syndrome

    a congenital abnormality of the central nervous system marked by failure of the midline structures of the cerebellum to develop, dilation of the fourth ventricle, and upward displacement of the transverse sinuses, tentorium, and torcula. clinical features include occipital bossing, progressive head enlargement, bulging of anterior fontanelle, papilledema, ataxia, gait disturbances, nystagmus, and intellectual compromise. (from menkes, textbook of child neurology, 5th ed, pp294-5)
  • Hydrocephalus

    excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial hypertension; headache; lethargy; urinary incontinence; and ataxia.
  • Hydrocephalus, Normal Pressure

    a form of compensated hydrocephalus characterized clinically by a slowly progressive gait disorder (see gait disorders, neurologic), progressive intellectual decline, and urinary incontinence. spinal fluid pressure tends to be in the high normal range. this condition may result from processes which interfere with the absorption of csf including subarachnoid hemorrhage, chronic meningitis, and other conditions. (from adams et al., principles of neurology, 6th ed, pp631-3)
  • Walker-Warburg Syndrome

    rare autosomal recessive lissencephaly type 2 associated with congenital muscular dystrophy and eye anomalies (e.g., retinal detachment; cataract; microphthalmos). it is often associated with additional brain malformations such as hydrocephaly and cerebellar hypoplasia and is the most severe form of the group of related syndromes (alpha-dystroglycanopathies) with common congenital abnormalities in the brain, eye and muscle development.
  • Cerebrospinal Fluid Rhinorrhea

    discharge of cerebrospinal fluid through the nose. common etiologies include trauma, neoplasms, and prior surgery, although the condition may occur spontaneously. (otolaryngol head neck surg 1997 apr;116(4):442-9)
  • External Hydrocephalus

    abnormal increase of cerebrospinal fluid in the subdural space of the brain.
  • Acquired Hydrocephalus

    hydrocephalus that results from head trauma, brain tumors, intracranial hemorrhage, or meningitis.
  • Cerebrospinal Fluid Rhinorrhea

    discharge of cerebrospinal fluid through the nose.

Index to Diseases and Injuries References

The following annotation back-references for this diagnosis code are found in the injuries and diseases index. The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10-CM code(s).

Convert G91.9 to ICD-9-CM

  • ICD-9-CM Code: 331.4 - Obstructiv hydrocephalus
    Approximate Flag - The approximate mapping means there is not an exact match between the ICD-10 and ICD-9 codes and the mapped code is not a precise representation of the original code.

Code History

  • FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
  • FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
  • FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.


[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.