leptomeningeal
Meaning of leptomeningeal: An adjective that quietly narrows the field to two of the three coverings, the pair the spinal fluid actually runs between.
Definition of leptomeningeal
Leptomeningeal describes anything relating to the two inner coverings of the brain and spinal cord, the arachnoid and the pia mater, known together as the leptomeninges. Cerebrospinal fluid circulates in the space between them. The word appears most often in leptomeningeal disease, where cancer or infection has spread through that fluid filled space.
Which layers does the word cover?
Three membranes wrap the brain and cord. The outermost is the dura mater, thick and leathery, and this word excludes it. The meninges beneath are the arachnoid, a delicate cobweb of strands, and the pia mater, a film so thin it follows every fold of the surface. Those two are the leptomeninges, and the fluid that cushions the brain flows in the gap between them. A separate word, pachymeningeal, refers to the thick outer layer, so the two terms divide the coverings between them.
Why does the distinction matter?
| Layer group | Membranes | What collects there |
|---|---|---|
| Leptomeninges | Arachnoid and pia mater | Cerebrospinal fluid and whatever it carries |
| Pachymeninx | Dura mater | Blood from torn vessels in subdural and epidural bleeds |
Bleeding tends to gather against the dura, while infection and spreading tumor travel in the fluid beneath the arachnoid. The distinction therefore predicts both what a scan will show and how far a problem can reach, since the fluid path runs over the whole brain and down the entire length of the spinal cord.
What is leptomeningeal disease?
Cancer cells that reach the cerebrospinal fluid are carried wherever it flows and settle in scattered deposits along the brain surface, the cranial nerves and the nerve roots. Because the deposits are spread out rather than massed in one lump, the effects are patchy and odd: double vision, a drooping face, hearing loss, headache and weakness in one limb can appear together. Spread of this kind from a solid tumor, called leptomeningeal metastasis, is seen most often with breast cancer, lung cancer and melanoma, and with leukemia and lymphoma among blood cancers. Bacterial meningitis inflames the same space, which is why the two can resemble each other on imaging.
How is it detected?
Two approaches, each imperfect. Scanning after contrast can show the membranes lighting up as thin lines along the surface and the roots. Sampling the fluid by spinal tap can show malignant cells directly, but one sample often misses them and repeat sampling raises the yield. A negative result therefore does not settle the question, and the diagnosis frequently rests on a suggestive scan combined with a matching pattern of symptoms.
Also known as
Used in a sentence
Contrast enhanced imaging showed leptomeningeal enhancement along the cerebellar folia.
Good to know
The word excludes the tough outer dura mater, so leptomeningeal spread describes disease traveling in the cerebrospinal fluid rather than a mass sitting against the inner skull.
Word origin
Where “leptomeningeal” comes from
From the Greek leptos, meaning slender or thin, with meninx, a membrane, marking the delicate inner coverings off from the thick outer one.