myelomeningocele is the most severe and most common form of open spina bifida, in which a portion of the spinal cord and its surrounding meninges herniate through a defect in the posterior vertebral arches, forming a fluid-filled sac visible on the newborn’s back. It is distinguished from meningocele, in which only the meninges (not neural tissue) protrude through the defect, and from spina bifida occulta, a closed form in which the vertebral defect exists without any herniation of spinal contents or a visible sac. The underlying mechanism is a failure of neural tube closure during the third to fourth week of gestation, leaving the developing spinal cord exposed and tethered rather than fully encased in bone and soft tissue. myelomeningocele is always pathological — unlike some congenital variants that can be asymptomatic, this defect exposes neural tissue directly, carrying a high risk of infection, CSF leak, and permanent neurologic injury without timely surgical closure. Clinically relevant subtypes are classified by anatomic level and by the presence or absence of associated hydrocephalus, most often coded as cervical (Q05.0, Q05.5), thoracic (Q05.1, Q05.6), lumbar (Q05.2, Q05.7), and sacral (Q05.3, Q05.8) spina bifida, with or without hydrocephalus. Myelomeningocele is frequently confused with Arnold-Chiari syndrome, but the two are distinct entities that commonly coexist — myelomeningocele is the spinal defect itself, while Arnold-Chiari (Chiari II) is the associated hindbrain herniation, coded separately under Q07.0.
“tumor,” “hernia,” “swelling” — suffix denoting a protrusion or herniation of tissue through a defect
The term entered medical English in the 19th century as myelomeningocele (noun), a compound coined directly from the Greek roots rather than borrowed through an intermediate language — literally “hernia of the spinal cord and its membranes.” The compound reflects the precise anatomy of the defect: unlike a simple meningocele (“hernia of membrane” alone), the myel- root signals that neural tissue itself is involved in the protrusion, marking the more severe form. The root mening- (“membrane”) connects this term to the entire -cele root family: encephalocele (herniation of brain tissue through a skull defect), meningocele (herniation of meninges alone), and rachischisis (complete failure of neural tube and spinal cord fusion, an even more severe variant). The suffix -cele is highly productive in surgical terminology, appearing in hydrocele, varicocele, cystocele, and rectocele.
🔀 ALIASES / ALTERNATE TERMS
Meningomyelocele(reversed-order synonym used interchangeably with myelomeningocele in some literature and documentation; refers to the identical anatomic entity)
Open spina bifida(lay and clinical term emphasizing the exposed, uncovered nature of the defect, as opposed to closed/occulta forms)
Spina bifida cystica(clinical synonym describing the visible cystic sac formed by the herniated spinal contents; encompasses both myelomeningocele and meningocele)
MMC(clinical abbreviation used commonly in neurosurgery, maternal-fetal medicine, and NICU documentation)
Myelocele(closely related but distinct term for a flat, non-cystic neural tube defect without a covering membrane, in which neural tissue is flush with the skin surface rather than forming a sac)
Cervical myelomeningocele(anatomic subtype at the cervical spine level; coded Q05.0 with hydrocephalus or Q05.5 without)
Thoracic myelomeningocele(anatomic subtype at the thoracic spine level; coded Q05.1 with hydrocephalus or Q05.6 without)
Lumbar myelomeningocele(anatomic subtype at the lumbar spine level, the most common location; coded Q05.2 with hydrocephalus or Q05.7 without)
Sacral myelomeningocele(anatomic subtype at the sacral spine level; coded Q05.3 with hydrocephalus or Q05.8 without)
đź”— RELATED TERMS
meningocele — the milder counterpart of myelomeningocele in which only the meninges, not neural tissue, herniate through the vertebral defect; carries a substantially lower risk of permanent neurologic deficit.
spina bifida occulta — the closed, often asymptomatic form of spina bifida in which a vertebral defect exists without any herniation of spinal contents or visible sac; coded Q76.0 and excluded (Excludes1) from the Q05 myelomeningocele family.
Arnold-Chiari syndrome — the hindbrain herniation (Chiari II malformation) that coexists with myelomeningocele in the vast majority of affected infants, coded separately under Q07.0; the two conditions are distinct but nearly always managed together.
hydrocephalus — the buildup of cerebrospinal fluid within the ventricles, present in the majority of myelomeningocele cases due to associated Chiari II malformation; drives selection between the “with hydrocephalus” and “without hydrocephalus” Q05 codes.
tethered cord syndrome — a common long-term complication in which the spinal cord becomes abnormally fixed at the level of the prior repair, causing progressive neurologic symptoms as the child grows; coded separately and often requires later untethering surgery.
neurogenic bladder — a frequent downstream manifestation of the spinal cord dysfunction caused by myelomeningocele, requiring lifelong urologic management and separate ICD-10-CM coding.
neural tube defect — the broader embryologic category to which myelomeningocele belongs, encompassing all conditions arising from failure of neural tube closure between the third and fourth weeks of gestation.
fetal myelomeningocele repair — an in-utero surgical intervention, increasingly used for eligible candidates, performed prior to birth to close the defect and reduce the severity of associated hindbrain herniation and hydrocephalus.
prenatal ultrasound — the primary diagnostic tool for identifying myelomeningocele in utero, typically confirmed with fetal MRI when surgical planning is being considered.
CODING CORNER
🏥 ICD-10-CM CODES
Spina Bifida with Hydrocephalus (Q05.0–Q05.4 — Site Specificity Required)
Unlisted fetal invasive procedure, including ultrasound guidance — used to report in-utero fetal myelomeningocele repair, since no dedicated CPT code currently exists for this procedure
⚠️ Coding Note: The Q05 category requires both anatomic site (cervical, thoracic, lumbar, sacral, or unspecified) and hydrocephalus status to reach a billable fourth-character code — never report the Q05 category header alone, and never default to the unspecified site code (Q05.9) when the operative note or imaging clearly documents a specific spinal level. Sequence the myelomeningocele code (Q05.x) as principal diagnosis on the newborn’s own record when it is the primary reason for the encounter; associated Arnold-Chiari findings (Q07.0 family) and manifestations such as paraplegia (G82.2x) or neurogenic bladder (N31.9) should be reported as secondary diagnoses when documented. A common undercoding alert on inpatient profee claims is capturing only the myelomeningocele repair CPT code while omitting the concurrent VP shunt placement (62223) performed in the same admission — review the operative log closely, since these are frequently staged procedures billed with modifier -58. In-utero fetal repair claims require the unlisted procedure code 59897 since no CPT code specific to fetal myelomeningocele closure currently exists, and most payers require extensive prior authorization documentation, including maternal-fetal medicine consultation notes and MOMS-trial-based eligibility criteria, before approving this intervention.