CorpusHuman Anatomy
NervousMembrane

Pia mater

Pia mater

Also known as: pia

The delicate, vascular innermost meninx closely applied to the brain and spinal cord, following every gyrus and sulcus; it forms the denticulate ligaments and filum terminale and, with ependyma, the tela choroidea.

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Overview

The pia is a thin layer of flattened cells and fine collagen that adheres to the glia limitans, the layer of astrocyte end-feet on the surface of the CNS. It follows the brain into every sulcus and fissure. Penetrating arteries carry a sleeve of pia a short way into the brain, creating the perivascular (Virchow–Robin) spaces, which take part in fluid and solute exchange (the "glymphatic" pathway).

In the spinal cord the pia is thicker and forms two anchoring structures:
• Denticulate ligaments: ≈21 pairs of tooth-like lateral extensions between the dorsal and ventral roots that attach to the dura and suspend the cord.
• Filum terminale: the pial strand continuing from the conus medullaris through the cauda equina to the dural sac (filum terminale internum) and then, ensheathed by dura, to the coccyx (filum terminale externum).
A longitudinal thickening over the anterior median fissure (the linea splendens) covers the anterior spinal artery. Where the pia meets the ependyma of the ventricular roof without intervening nervous tissue, it forms the tela choroidea, which is invaginated by capillaries to form the choroid plexus.

Location

Innermost meninx, directly on the surface of the brain and spinal cord.

Parts & subdivisions

  1. Denticulate ligaments
    ≈21 pairs of lateral pial extensions anchoring the spinal cord to the dura; landmark for anterolateral cordotomy (between the roots).
  2. Filum terminale
    Pial continuation of the conus to the coccyx.
  3. Tela choroidea
    Pia + ependyma in the ventricular roofs; forms the choroid plexus.
  4. Perivascular (Virchow–Robin) spaces
    Pia-lined sleeves around penetrating vessels; enlarged spaces are a common MRI finding.

Anatomy

Histology

One to a few layers of flattened pial cells over a thin collagen and elastic layer resting on the basal lamina of the glia limitans.

Function

  • Covers and supports the CNS surface and its vessels
  • Anchors the spinal cord (denticulate ligaments, filum terminale)
  • Contributes to the choroid plexus (tela choroidea)
  • Forms the inner wall of the subarachnoid space

Clinical significance

Leptomeningeal metastases

Cancers (breast, lung, melanoma, lymphoma, leukaemia) can seed the pia and arachnoid ("carcinomatous meningitis"). They cause multifocal cranial-nerve palsies, radiculopathies, headache and hydrocephalus. Gadolinium MRI shows linear enhancement following the sulci, and CSF cytology shows malignant cells.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.