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Langerhans Cell Histiocytosis, Skull and Brain


KEY FACTS

Terminology

  • Langerhans cell histiocytosis (LCH)

  • LCH now best understood as neoplastic disease

    • Activating somatic BRAF mutations, LCH cell clonality

Imaging

  • NECT

    • Sharply marginated lytic skull defect

      • –

        Beveled edges

    • Mastoid: Geographic destruction, soft tissue mass

  • MR

    • Absent posterior pituitary “bright spot” on T1WI

    • Thick enhancing infundibulum

    • Enhancing masses in choroid plexus, leptomeninges, basal ganglia

    • Sometimes cerebellar white matter disease

Top Differential Diagnoses

  • Lytic calvarial lesions

    • Surgical (burr hole, shunt, surgical defect)

    • Epidermoid

    • Dermoid

  • Pituitary infundibular/hypothalamic thickening, enhancement

    • Germinoma; metastasis; pituicytoma; neurosarcoid

Clinical Issues

  • Can be confined only to skull (often asymptomatic) but can involve other tissues also (skin, lymph glands, lungs, CNS); if > 1 organ involved, may have symptoms

Diagnostic Checklist

  • Calvaria is most frequent bony site involved by LCH

  • Thick enhancing pituitary stalk is most common CNS manifestation of LCH

    • If initially “normal” MR in patient with diabetes insipidus, repeat in 2-3 months

  • Consider LCH for ataxic patient with choroid plexus masses, cerebellar white matter demyelination

Lateral graphic demonstrates 3 sharply defined lytic lesions
of the membranous calvaria with geographic destruction. Note the beveled margins of the bony lysis
.

Lateral radiograph in a 3-year-old boy with several subcutaneous masses and central diabetes insipidus demonstrates multiple lytic lesions of the skull
. Note the “cookie cutter” sharp pattern of bony lysis and the beveled edge pattern
of differential inner and outer table calvarial involvement.

Axial NECT in a 5-year-old girl with multiple scalp masses demonstrates 2 lytic lesions
of the left frontal bone. Both lesions show the characteristic pattern of sharply defined geographic bony lysis. Note the unequal inner and outer table involvement creating a beveled edge appearance.

Axial NECT in a proptotic 10-year-old boy shows a sharply defined lytic lesion of the lateral orbital wall
. Note the soft tissue mass displacing the lateral rectus muscle
.

TERMINOLOGY

Synonyms

  • Langerhans cell histiocytosis (LCH)

    • Several entities (eosinophilic granuloma, Hand-Schuller-Christian disease, Letterer-Siwe disease, and “histiocytosis X” now under single designation of LCH

Definitions

  • LCH now best understood as neoplastic disease

    • Activating somatic BRAF mutations, LCH cell clonality

    • Inflammatory myeloid neoplasia

  • Divided into 3 groups (based on number of lesions, systems involved)

    • Unifocal (localized) form

      • –

        70% of cases

      • –

        Limited to single or a few bones, may involve lung

    • Multifocal unisystem

      • –

        20% of cases

      • –

        Chronic, recurring

      • –

        Multiple bones, reticuloendothelial system, pituitary/hypothalamus

    • Multifocal, multisystem

      • –

        10% of cases

      • –

        Fulminant (often fatal)

IMAGING

General Features

  • Best diagnostic clue

    • Calvaria: Sharply marginated lytic skull defect with beveled margins

    • Skull base (mastoid most common): Geographic destruction ± soft tissue mass

    • Brain: Thick enhancing infundibulum, absent posterior pituitary bright spot on T1WI

  • Location

    • Calvaria

      • –

        Most common bony site

        • □

          Frontal, parietal bones > temporal, occipital

      • –

        Also mastoid portion of temporal bone, mandible, orbit, facial bones

    • Brain: Pituitary gland/infundibulum, hypothalamus

      • –

        Rare: Choroid plexus, leptomeninges, basal ganglia, cerebellar white matter (WM), and brain parenchyma

  • Size

    • Skull and facial bones: May grow, coalesce

    • Pituitary infundibulum: Small lesions due to early endocrine dysfunction (central DI)

  • Morphology

    • Variable patterns of bony lysis (“geographic” skull)

    • Soft tissue masses vary from discrete ↔ infiltrative

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