glioblastoma

DEFINITION of glioblastoma

glioblastoma is the most common and most aggressive primary malignant brain tumor in adults, arising from glial precursor cells (astrocytic lineage) and classified by the WHO as a Grade 4 diffuse astrocytic glioma. It is distinguished from lower-grade astrocytoma and oligodendroglioma by its marked cellular anaplasia, microvascular proliferation, and characteristic pseudopalisading necrosis on histopathology. The underlying mechanism involves uncontrolled proliferation of glial precursor cells with molecular alterations such as IDH-wildtype status, EGFR amplification, and 1p/19q intact profile, driving rapid infiltrative growth into surrounding brain parenchyma. glioblastoma is always pathologic — there is no physiologic counterpart — and it is coded under the malignant neoplasm of brain category depending on anatomic site (e.g., frontal lobe, C71.1; temporal lobe, C71.2; unspecified site, C71.9). It is commonly confused with metastatic brain lesions coded as secondary malignant neoplasm of brain (C79.31), the key difference being that glioblastoma originates within brain tissue itself rather than spreading from a distant primary cancer.

---

ETYMOLOGY of glioblastoma

greek

Component	Origin	Meaning
o-	Greek glia (γλία)	“glue” — refers to the glial (connective/supportive) cells of the nervous system
-blast-	Greek blastos (βλαστός)	“germ,” “immature cell,” “budding/growing cell” — denotes an immature precursor cell
-oma	Greek -oma (-ωμα)	Noun-forming suffix — “tumor,” “swelling”

The word entered English in the 1920s as glioblastoma (noun), a modern medical coinage built directly from Greek roots rather than borrowed through an intermediate language, from Greek glia (“glue”) plus blastos (“germ, immature cell”) plus -oma (“tumor”) — literally “tumor of immature glue-cells.” The root glia connects glioblastoma to the entire glio- root family: glioma (tumor of glial cells generally), glial cell (supportive nervous-system cell), and glial fibrillary acidic protein (a diagnostic marker). The combining form glio- is highly productive in neuro-oncology terminology, appearing in glioma, gliosis, glioneuronal tumor, astrocytoma, and oligodendroglioma.

---

🔀 ALIASES / ALTERNATE TERMS

• Glioblastoma multiforme (GBM) (older, still widely used clinical name reflecting the tumor’s variable histologic appearance)
• Grade 4 astrocytoma, IDH-wildtype (current WHO CNS5 classification term emphasizing molecular subtype)
• High-grade glioma (broader lay/clinical term encompassing glioblastoma and other Grade 3-4 gliomas)
• Secondary glioblastoma (subtype arising from progression of a pre-existing lower-grade astrocytoma, typically IDH-mutant)
• Primary glioblastoma (de novo subtype arising without a prior lower-grade precursor lesion, typically IDH-wildtype)
• Giant cell glioblastoma (histologic variant with numerous multinucleated giant cells; coded under C71.9 with morphology noted in pathology report)
• Gliosarcoma (variant with both glial and sarcomatous mesenchymal components)
• Butterfly glioma (descriptive term for glioblastoma crossing the corpus callosum bilaterally, involving both cerebral hemispheres; coded C71.8)
• Brain stem glioblastoma (anatomic subtype; C71.7)
• Cerebellar glioblastoma (anatomic subtype; C71.6)
• Frontal lobe glioblastoma (anatomic subtype; C71.1)
• Temporal lobe glioblastoma (anatomic subtype; C71.2)

---

🔗 RELATED TERMS

• meningioma — a typically benign tumor of the meningeal lining rather than glial tissue; distinguished from glioblastoma by its extra-axial (outside brain parenchyma) origin and slower growth.
• Glioma — shares the o- root; the general category of tumors arising from glial cells, of which glioblastoma is the highest-grade form.
• Astrocytoma — lower-grade precursor lesion (WHO Grade 2-3) that may progress to secondary glioblastoma; distinguished by lower mitotic activity and absence of necrosis.
• Secondary malignant neoplasm of brain — metastatic brain lesion from a distant primary cancer, overlapping in presentation (headache, seizure, focal deficit) but coded as C79.31 with the primary site coded first.
• Microvascular proliferation — the abnormal new blood vessel formation within the tumor that is a defining histologic hallmark distinguishing glioblastoma from lower-grade gliomas.
• Pseudopalisading necrosis — characteristic pattern of tumor cells arranged around necrotic zones, a required histologic feature for glioblastoma diagnosis.
• IDH-wildtype status — molecular mechanism/marker distinguishing primary (de novo) glioblastoma from IDH-mutant astrocytomas that secondarily progress to Grade 4.
• Gliosarcoma — disease entity with mixed glial and sarcomatous differentiation; coded under C71.9 with morphologic notation.
• Diffuse midline glioma, H3 K27-altered — related pediatric/young-adult high-grade glioma entity with distinct molecular driver; coded under site-specific C71 codes (e.g., brain stem, C71.7).
• Radiation necrosis — a treatment-related complication that can mimic tumor recurrence on imaging, commonly requiring differentiation from true glioblastoma progression.
• Pseudoprogression — imaging phenomenon following chemoradiation that mimics tumor growth, clinically distinguished from true progression via serial MRI.
• MRI brain with contrast — primary diagnostic and surveillance imaging modality for evaluating glioblastoma and its treatment response.

---

CODING CORNER

🏥 ICD-10-CM CODES

Primary Malignant Neoplasm of Brain by Site (Glioblastoma — C71.-)

Code	Description
C71.0	Malignant neoplasm of cerebrum, except lobes and ventricles
C71.1	Malignant neoplasm of frontal lobe
C71.2	Malignant neoplasm of temporal lobe
C71.3	Malignant neoplasm of parietal lobe
C71.4	Malignant neoplasm of occipital lobe
C71.5	Malignant neoplasm of cerebral ventricle
C71.6	Malignant neoplasm of cerebellum
C71.7	Malignant neoplasm of brain stem
C71.8	Malignant neoplasm of overlapping sites of brain (e.g., butterfly glioma)
C71.9	Malignant neoplasm of brain, unspecified — most frequently used code when specific lobe/site is not documented

Differential / Related Neoplasm Codes

Code	Description
D33.2	Benign neoplasm of brain, unspecified
D43.2	Neoplasm of uncertain behavior of brain, unspecified
C79.31	Secondary malignant neoplasm of brain and cerebral meninges — used for metastatic disease, not primary glioblastoma

History & Encounter Codes

Code	Description
Z85.841	Personal history of malignant neoplasm of brain
Z51.0	Encounter for antineoplastic radiation therapy
Z51.11	Encounter for antineoplastic chemotherapy

Associated Neurologic Manifestations

Code	Description
G93.89	Other specified disorders of brain
G40.909	Epilepsy, unspecified, not intractable, without status epilepticus
R56.9	Unspecified convulsions

---

🔧 COMMON CPT CODES (Glioblastoma-Related Diagnosis & Treatment)

CPT Code	Description
61140	Burr hole(s) or trephine; with biopsy of brain or intracranial lesion
61751	Stereotactic biopsy, aspiration, or excision, including burr hole(s), for intracranial lesion; with computed tomography and/or magnetic resonance guidance
61510	Craniectomy, trephination, bone flap craniotomy; for excision of brain tumor, supratentorial, except meningioma
61518	Craniectomy for excision of brain tumor, infratentorial or posterior fossa; except meningioma, cerebellopontine angle tumor, or midline tumor at base of skull
61517	Implantation of brain intracavitary chemotherapy agent (e.g., carmustine wafer) at time of craniotomy
70551	MRI brain without contrast
70552	MRI brain without contrast, followed by contrast and further sequences
70553	MRI brain without contrast, then with contrast and further sequences (single session)
77301	Intensity-modulated radiotherapy plan, including dose-volume histograms for target and critical structure partial tolerance specifications
77402	Radiation treatment delivery; Level 1, including imaging guidance, when performed
77407	Radiation treatment delivery; Level 2, single-isocenter (e.g., 3D or IMRT), photons, including imaging guidance, when performed
77412	Radiation treatment delivery; Level 3, multiple isocenters with photon therapy or single-isocenter with active motion management, including imaging guidance, when performed
96413	Chemotherapy administration, intravenous infusion technique; up to 1 hour, single or initial substance/drug (e.g., bevacizumab)
96415	Chemotherapy administration, intravenous infusion technique; each additional hour

---

⚠️ Coding Note: glioblastoma requires the most anatomically specific C71 code the documentation supports (e.g., frontal lobe C71.1 over unspecified C71.9); when the tumor crosses the corpus callosum bilaterally, use C71.8 for overlapping sites rather than defaulting to unspecified. Sequence the malignant neoplasm code first at the initial encounter, with Z51.0 or Z51.11 added for pure treatment-only encounters once the malignancy is already established and being treated. A frequently undercoded scenario on inpatient profee claims is carmustine wafer (Gliadel) implantation performed at the same operative session as tumor resection — this is separately reportable with 61517 in addition to the craniotomy code and should trigger a query if the operative note mentions “wafer” or “carmustine” without a corresponding charge. For radiosurgical or fractionated radiation delivered under the revised 2026 CPT structure, confirm whether the payer requires the professional-component modifier -26 on 77387 separately from the global treatment delivery codes 77402, 77407, or 77412, since the old 77385/77386/77014/G-code structure was fully retired effective January 1, 2026. For prolonged or technically complex craniotomies (e.g., awake mapping, eloquent cortex involvement), modifier -22 (increased procedural services) should be considered with strong documentation support, and co-surgeon cases (e.g., neurosurgery plus ENT for skull base approach) should carry modifier -62 on both surgeons’ claims.

---

DERIVATIONS of glioblastoma

TABLE definition AS Definition
FROM #medterm 
WHERE length(filter(roots, (word) => econtains([[glioblastoma]].roots, word))) > 0 AND file.name != [[glioblastoma]].file.name
SORT file.name ASC

---

Query functionality

TABLE definition AS Definition
FROM #medterm 
WHERE length(filter(definition, (word) => econtains([[glioblastoma]].definition, word))) > 0 AND file.name != [[glioblastoma]].file.name

Med terms dictionary Appendix A Prefixes Appendix B Combining Forms Appendix C Suffixes Appendix D Suffix forms