Cerebellum and Brainstem: Diagnosis



Cerebellum and Brainstem: Diagnosis










Glial tumors are the most common primary tumor of the cerebellum and brainstem. This diffuse pontine glioma compresses the 4th ventricle image and surrounds the basilar artery image.






A diffuse astrocytoma is characterized by irregular, dark, hyperchromatic ovoid or fusiform nuclei with inconspicuous nucleoli image sitting in a fibrillar background image.


SURGICAL/CLINICAL CONSIDERATIONS


Goal of Consultation



  • Diagnosis to determine appropriate intraoperative and postoperative treatment



    • Resection (e.g., ependymoma)


    • Biopsy for diagnosis followed by treatment with radiotherapy or chemotherapy (e.g., medulloblastoma)


  • Proper handling of tissue for ancillary studies (i.e., molecular studies, electron microscopy, microbiologic culture)


Change in Patient Management



  • Immediate intraoperative planning, as well as diagnostic tissue allocation


Clinical Setting



  • 3 main clinical scenarios requiring tissue sampling



    • Patients with symptoms and signs of increased intracranial pressure, such as nausea and vomiting



      • Urgent surgery to prevent impending herniation


    • Patients with chronic or subacute symptoms, such as ataxia and seizures



      • Biopsy to diagnose a slow-growing or insidious process


    • Patients with specific cranial nerve palsies or hearing loss



      • Indicative of subarachnoid involvement by inflammatory or metastatic infiltrates or local pressure by mass lesions such as vestibular schwannomas


      • Biopsy to diagnose disease process


Neuroimaging



  • Review of imaging studies is important to determine most likely differential diagnosis for a lesion


  • Neuroanatomic localization



    • Cerebellar hemisphere: Pilocytic astrocytomas in children, metastases and hemangioblastomas in adults


    • Cerebellar midline: Medulloblastomas in children


    • 4th ventricle: Ependymomas in children, subependymomas in adults


    • Cerebellopontine angle: Choroid plexus tumors and ependymomas in children, vestibular schwannomas and meningiomas in adults


  • Signal characteristics



    • Cysts with mural nodules in pilocytic astrocytomas, hemangioblastomas


    • Contrast enhancement in pilocytic astrocytomas and medulloblastomas (heterogeneous), metastases, and abscesses (rim pattern)


    • Decreased diffusion in infarcts, hemorrhages


    • Ill-defined, nonenhancing hemispheric lesions in low-grade gliomas


    • Rim enhancing after contrast administration in glioblastomas, lymphomas, toxoplasmosis


SPECIMEN EVALUATION


Gross



  • Usually very few distinctive macroscopic features



    • Gliomas: Soft, gray-translucent, gelatinous texture


    • Pilocytic astrocytomas: Firm, rubbery, white-tan


    • Choroid plexus tumors: Papillary fronds, prominent vasculature


    • Hemangioblastomas: Vascular, hemorrhagic


    • Vestibular schwannomas, meningiomas: Firm, fibrous, or rubbery, gray-tan; difficult to smear


    • Abscesses: Purulent, sometimes with fibrous wall


    • Many lesions are hemorrhagic (nonspecific)


  • Distinguish lesional from normal for frozen section and smear preparation



    • Brainstem, cerebellar tissue: Soft pink-white, easily smeared as thin uniform film


    • Meningeal tissue: Membranous, vascular, does not smear well


    • White matter: Pearly white, sticky, but smears well


    • Metastases: Granular or mucoid, pink, gray, tan-yellow or hemorrhagic, depending on type; smears in clumps



    • Gliomas: Usually more gray and mucoid, smears well or in strings


Frozen Section



  • Important not to use entire specimen (may be only specimen received)



    • Do smear cytologic prep 1st


    • Use ˜ 1 mm of tissue from both ends of core biopsy to represent proximal and distal to lesion


  • Frozen method



    • Perch tissue to be frozen on small bead of embedding medium, do not cover with medium


    • If core biopsy, bisect sample longitudinally, after ends were taken for smears, and freeze 1/2


    • Freeze quickly with light touch of metal heat extractor or cryospray to avoid ice crystals in tissue


    • Step section carefully into block when making slides


  • In some cases, cytologic preparations only may be preferable



    • Small specimens, suspected infectious disease, or calcified lesions


Cytology



  • Smear (squash) for soft specimens, works for most samples


  • 2 or 3 ˜ 1 mm pieces may be used to represent different sites on same slide


  • Touch preparation for firm/fibrous/calcified lesions


  • Scan entire slide, as lesions may be heterogeneous


Allocation For Special Studies



  • Glial tumors, some metastatic tumors (lung, colon)



    • Reserve frozen tissue for molecular studies


    • Required by some cancer centers for clinical trial eligibility


  • Infectious specimens



    • Tissue should be sent for microbiologic cultures


    • Sterile tissue sent directly from operating room is preferable for this purpose


MOST COMMON DIAGNOSES


Diffuse Brainstem Glioma



  • Frozen section



    • Rarely biopsied


    • Features of diffuse astrocytoma, ± anaplasia


  • Smear



    • Hyperchromatic, ovoid or fusiform nuclei


    • Fibrillary background


    • No Rosenthal fibers


    • Microvascular proliferation in anaplastic tumors


    • Necrosis suggests glioblastoma, unless prior radiotherapy


  • Difficulties



    • Usually extremely small samples


Pilocytic Astrocytoma



  • Frozen section



    • Dense areas with fibrillary background containing Rosenthal fibers and eosinophilic granular bodies, alternating with loose, microcystic regions



      • Rosenthal fibers are thick, eosinophilic twisted fibers (comprised of intermediate filaments)


    • Oval nuclei with occasional pleomorphism, rare or no mitoses


    • Frequent microvascular proliferation of no prognostic significance


    • Necrosis rare (suggests alternative diagnosis)


  • Smear



    • Clear bipolar cytomorphology


    • Network of coarse Rosenthal fibers in background and eosinophilic granular bodies


    • Knots of microvascular proliferation


  • Difficulties



    • If sample very small, may not have all desired features


    • Report as “astrocytoma with piloid features”


Medulloblastoma



  • Frozen section



    • “Small blue cell tumor” with broad regions of solid tumor


    • Single-cell apoptosis and geographic necrosis


    • High mitotic rate


    • Variable features



      • Homer Wright rosettes (classical medulloblastoma)


      • Connective tissue septa creating nodular pattern (desmoplastic medulloblastoma)


      • Large, bizarre cells with prominent nucleoli (anaplastic/large cell medulloblastoma)


      • Not necessary to distinguish variants intraoperatively


  • Smear



    • Uniform oval or carrot-shaped nuclei with little cytoplasm


    • Dirty necrotic background with nuclear fragments


    • Usually, conspicuous mitoses


    • Distinguish from normal cerebellar granule cells (smaller, uniformly round, bland)


  • Difficulties



    • Indistinguishable from atypical teratoid/rhabdoid tumor on intraoperative consultation


    • Report as “small blue cell tumor, diagnosis deferred to permanent sections”


    • If smear is too aggressive, nuclei may disrupt in chromatin clumps and streaks


    • Normal hypercellular granular cell layer of cerebellar cortex may confuse interpreter if unaware


Atypical Teratoid/Rhabdoid Tumor (AT/RT)



  • Frozen section



    • “Small blue cell tumor” without rosettes


    • Variably conspicuous rhabdoid cells with abundant, dense, eosinophilic cytoplasm


    • Occasional clear cells and “cannibal” cells (one cell engulfing another)


  • Smear



    • Predominantly uniform oval or carrot-shaped nuclei with little cytoplasm


    • Rhabdoid cells better seen on smear than frozen section


    • Nuclear debris and (usually) high mitotic rate


  • Difficulties



    • Indistinguishable from medulloblastoma on intraoperative consultation


    • Report as “small blue cell tumor, diagnosis deferred to permanent sections”


Ependymoma



  • Frozen section




    • Variably cellular, with perivascular pseudorosettes, ependymal tubules or canals, and small intracytoplasmic vacuoles (lumina)


    • Microvascular proliferation of no prognostic significance (WHO grade II)


    • Marked cytologic atypia, mitoses, and necrosis indicate anaplastic ependymoma (WHO grade III)


  • Smear



    • Glial tumor cells with uniform oval nuclei, often with small nucleoli and slightly granular chromatin


    • Cytoplasmic processes, radially arranged around blood vessels, ± vascular cell proliferation


    • Occasional intracytoplasmic lumina, as well as cilia and terminal bars (blepharoplasts) in tubules


  • Difficulties



    • Must establish diagnosis with reasonable certainty, as resection is definitive therapy (unlike medulloblastoma or AT/RT)


    • Grading may not be reliable due to tumor heterogeneity


    • Presence of microvascular proliferation and occasional necrosis in some grade II ependymomas


    • Report as “ependymoma, grading deferred to permanent sections” (unless obviously anaplastic)


Schwannoma

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Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Cerebellum and Brainstem: Diagnosis

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