2026 ICD-10-CM Diagnosis Code D42.9Neoplasm of uncertain behavior of meninges, unspecified

AHRQ’s CCSR groups this code into broader clinical categories.

• Arachnoid

  a delicate membrane enveloping the brain and spinal cord. it lies between the pia mater and the dura mater. it is separated from the pia mater by the subarachnoid cavity which is filled with cerebrospinal fluid.

• Arachnoid Cysts

  intracranial or spinal cavities containing a cerebrospinal-like fluid, the wall of which is composed of arachnoidal cells. they are most often developmental or related to trauma. intracranial arachnoid cysts usually occur adjacent to arachnoidal cistern and may present with hydrocephalus; headache; seizures; and focal neurologic signs. (from joynt, clinical neurology, 1994, ch44, pp105-115)

• Arachnoiditis

  acute or chronic inflammation of the arachnoid membrane of the meninges most often involving the spinal cord or base of the brain. this term generally refers to a persistent inflammatory process characterized by thickening of the arachnoid membrane and dural adhesions. associated conditions include prior surgery, infections, trauma, subarachnoid hemorrhage, and chemical irritation. clinical features vary with the site of inflammation, but include cranial neuropathies, radiculopathies, and myelopathies. (from joynt, clinical neurology, 1997, ch48, p25)

• Medulloblastoma

  a malignant neoplasm that may be classified either as a glioma or as a primitive neuroectodermal tumor of childhood (see neuroectodermal tumor, primitive). the tumor occurs most frequently in the first decade of life with the most typical location being the cerebellar vermis. histologic features include a high degree of cellularity, frequent mitotic figures, and a tendency for the cells to organize into sheets or form rosettes. medulloblastoma have a high propensity to spread throughout the craniospinal intradural axis. (from devita et al., cancer: principles and practice of oncology, 5th ed, pp2060-1)

• Meninges

  the three membranes that cover the brain and the spinal cord. they are the dura mater, the arachnoid, and the pia mater.

• Meningocele

  a congenital or acquired protrusion of the meninges, unaccompanied by neural tissue, through a bony defect in the skull or vertebral column.

• Pia Mater

  the innermost layer of the three meninges covering the brain and spinal cord. it is the fine vascular membrane that lies under the arachnoid and the dura mater.

Anatomical sites in the Table of Neoplasms that reference this code family.

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Spinal Cord Diseases

Your spinal cord is a bundle of nerves that runs down the middle of your back. It carries signals back and forth between your body and your brain. It is protected by your vertebrae, which are the bone disks that make up your spine.

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