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Flashcards in Unknowns Deck (22):

Young male with chest wall mass.

Right image is stain for CD34.

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Solitary Fibrous Tumor (SFT)

  • Loose look
  • Pale pink at low power
  • Monomorphic/bland cells
  • Vascular
  • Staghorn forms
  • Stains:
    • STAT6 +
    • BCL2 +/-


Extremity mass in young child.

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  • Lots of lipoblasts and lipocytes within a myxoid matrix.
  • Lots of fat and myxoid areas within muscle
  • Delicate, curvilinear vessels
  • Ddx:
    • Myxoid liposarcoma
    • Lipoblastoma
  • Doesn't need to have lipoblasts
  • Gene: PLAG1
    • Also seen in pleomorphic adenoma


Soft tissue, forearm mass growing over last few weeks, male.

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Nodular fasciitis

  • Subq mass
  • Blue, spindled, cellular mass 
  • lighter and darker staining areas
  • Biphasic:
    • Lighter: tissue culture appearance
    • Darker: more cellular, spindled
  • Extravasated RBCs
  • MYH9/USP6
  • May become more cellular/less myxoid/less tissue culture-like over time

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Elderly person, bedridden, near sacrum

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Ischemic fasciitis

  • Benign, reactive
  • Fibrinoid necrosis is key
  • Usually not well circumscribed
  • Fibroblastic/myofibroblastic, ganglion like cells
    • Ganglion-like cells characteristic
  • AKA atypical decubital fibroplasia


Digit mass in young person with history of trauma.

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Myositis Ossificans

  • Immature, woven bone within muscle
  • Osteoblasts at periphery of trabeculae
  • Surrounding fibroblasts/myofibroblasts
  • Often seen with trauma
  • Ddx:
    • Parosteal osteosarcoma
    • BPOP

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30yo M w/ mass in thigh

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Prolferative Myositis/fasciitis

  • Loose, myxoid bands of fibrous tissue b/w muscle
  • "Checkerboard pattern"
  • Extravasated RBCs
  • Few atypical mitoses
  • Related to nodular fasciitis
  • Shares many features with and may be continuous with/variant of proliferative fasciitis (below)

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Young adult with HIV.

S-100 and CD68 positive.

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Mycobacterial Spindle Cell Pseudotumor

  • Spindled lesion
  • Vesicular, oval cells w/ indistinct cell borders
  • Vaguely storiform
  • Scattered giant cells
  • Stains:
    • SMA, FLY1, ERG -
    • Desmin -
    • CD31/34 -
    • HHV8 -
    • CD3/20 -
    • CD68 +
    • CD163 +
    • AFB +


60 year old male w/ dorsal hand biopsy

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Colloid milium

  • Dermal "goo"
  • Amorphous pink material with cracking in b/w
  • Hands and face
  • Older people


Infant with rapidly progressive brain mass

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Atypical Teratoid Rhabdoid Tumor (ATRT)

  • Pleomorphic cells on smear (brain)
  • Pink bellies (rhabdoid)
  • Loss of INI-1
  • PNET component in 65%
  • Spindled cells or even chondroid foci may be seen
  • Vimentin, EMA+, CK+, actin + in majority of cases
  • SYN+, GFAP + in some cases
  • b-HCG−, PLAP− (i.e., not a germ cell tumor despite occasional
  • alpha fetoprotein+)


10 year old w/ syndrome, scales on back, mentally retarded, mother w/ kidney lesion

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Angiofibroma (tuberous sclerosis)

  • Brain tumors: SEGA
  • Subependymal giant cell astrocytoma (SEGA) tumor
  • Tubers (cortical dysplasias)
  • Looks like 'spilling wax' on cross sxn
  • Usually have seizures
  • TSC1 and TSC2
  • Hamarin and tuberin
  • Ch 9 and 16
  • Mnemonic: SALSA HEART
    • Shagreen patches.
      • Shagreen patch = connective-tissue nevus composed of collagen, i.e. collagenoma.
    • Ash Leaf spots.
    • SEGA.
    • Angiofibroma.
    • Hamartomas.
    • Epilepsy.
    • Angiomyolipoma.
    • Rhabdomyoma.
    • Tubers.


Child with slowly growing, posterior fossa mass.  Cyst with mural nodule on imaging.

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Rosenthal Fibers (Pilocytic Astrocytoma)

  • Classically biphasic (though either may be absent):
    • Fibrillar.
    • Microcystic/loose.
  • Hair-like fibres ~ 1 micrometer; pilo- = hair.
    • Best seen on smear or with GFAP IHC.
  • Rosenthal fibres - key feature.
    • May be rare. Not pathognomonic.
  • Eosinophilic granular bodies.
  • Low cellularity - when compared to medulloblastoma and ependymoma.

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67 yo inguinal LAD; negative flow

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Hodgkin's Lymphoma

  • Doesn't flow bc too few cells
  • 45 NEG, 15/30 POS, DIM 20 (non classical is 15/30/45 switched)
  • lymphoid tissue outside of node is soft sign of lymphoma
  • PAX5 (should be dim)
  • Alk (for Anaplastic large cell lymphoma)
  • CD3/4/8 for T cells

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47yo F axillary LAD, NEG flow 

Keratin NEG and CD45 NEG

Vimentin POS

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Anaplastic Large (T) Cell Lymphoma

  • Large cells with eosinophilic cytoplasm.
    • Usually appear cohesive.
    • May be subcapsular in a lymph node and mimic a carcinoma.
  • Hallmark cells = "horseshoe-shaped or donut-shaped nucleus + eosinophilic paranuclear region" - key feature.
    • The donut-shaped version is also known as a "wreath cell" - large (multi-nucleated) cells with (morphologically) one toroidal-shaped nucleus.
  • DDx:
    • Hodgkin's lymphoma.
    • Carcinoma.


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63yo F diffuse LAD; monoclonal CD5-CD10- B cell population by flow

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Crystal Storage Histiocytoma

  • Foreign material (refractive like crystals)
  • Doesn't polarize
  • Strongly kappa positive
  • Associated with MGUS/Myeloma (MYD88 can diff bw LPL (+) and MM)


52yo M persistent LAD; negative flow

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Castleman's Disease

  • Day of:
    • Uni vs multi centric Castleman's
    • Stains:
      • CD138+
      • kappa/lambda to diff
      • HHV8 stain for multi centric Castleman's
    • Associations:
      • POEMS
      • Autoimmune disease
      • IgG4
      • Hyaline vascular type associated with follicular dendritic sarc
  • Pale concentric (expanded) mantle zone lymphocytes - key feature.
    • "Regressed follicles" - germinal center (pale area) is small.
  • "Lollipops":
    • Germinal centers fed by prominent (radially penetrating sclerotic) vessels; lollipop-like appearance.
  • Two germinal centers in one follicle.
  • Hyaline material (pink acellular stuff on H&E) in germinal center.
  • Sinuses effaced (lost).
  • Mitoses absent.

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4yo M w/ anemia

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Hereditary Pyropoikilocytosis

  • HE: Group of inherited disorders that have elliptical RBCs on peripheral blood smear
    • Can be categorized into 3 major groups based on RBC morphology
      • Common HE
      • Spherocytic HE (also called hemolytic ovalocytosis)
      • SAO
  • Molecular basis of HE is heterogeneous with defects found in several proteins
    • α-Spectrin and β-spectrin, protein 4.1R, GPC, band 3
  • Common HE
    • Peripheral blood smear shows > 30% biconcave elliptocytes and, in some patients, rod-shaped cells
    • Includes hemolytic HE and hereditary pyropoikilocytosis (HPP)
      • Peripheral blood smear shows marked anisopoikilocytosis with RBC fragments, microspherocytes, and poikilocytes
      • Similar changes in patients are also seen secondary to severe thermal injury/burns

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9yo w/ anemia, jaundice and 'fast-moving' Hb on electrophoresis

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Hemoglobin H Disease

  • Clinical Diagnosis
    • Clinical findings include splenomegaly, jaundice, and symptoms of anemia
    • α-Globin genes are located on chromosome 16
    • Dominant hemoglobin in adults, Hb A (approximately 96%) is composed of 2 α subunits and 2 β subunits (α₂β₂)
      • Hb H disease results in deletion of 3 of the 4 α genes (--/-α)
      • This leads to reduced production of α chains and excess production of β chains because β chains do not have α chains to polymerize and form Hb A
      • Excess β chain production leads to formation of β-tetramers, which cause membrane damage and hemolysis
  • Laboratory Diagnosis
    • MCV and MCH are low, and RBCs are increased
    • On electrophoresis and HPLC, Hb A₂ is decreased and Hb H is increased in adults
    • Hb Barts (tetrameric γ chains) is increased in neonates up to 40% at birth, then decreases to average of 5%
    • Blister cells on smear (previous image)

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6 month old w/ fever

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Gangliosidosis (Storage Disease)

  • Previous image:
    • A. a vacuolated lymphocyte
    • B. eosinophil with enlarged and sparse granules.
  • Large, sharply defined vacuoles in mature lymphocytes may suggest any of several lysosomal storage diseases.
    • The additional finding of the abnormal eosinophilic granulation is characteristic of GM1 gangliosidosis specifically.
    • GM1 gangliosidosis is an autosomal recessive lysosomal storage disorder caused by mutations in the GLB1 gene, which codes for β-galactosidase.
    • The incidence is estimated to be between 1 in 100 000 to 200 000 live births.
    • Type I is the most severe form and results in neurologic impairment caused by accumulation of GM1 gangliosides, typically within the first 6 months of life.
      • Other features include:
        • macular cherry-red spot
        • coarse facies
        • hepatosplenomegaly
      • Vacuolated lymphocytes and eosinophils with abnormally sparse and enlarged granules are characteristic findings in the peripheral smear. 

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1 month old w/ anemia.  Smear demonstrated smudge cells.

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  • General
    • Rare.
    • Genetic - may be autosomal dominant, autosomal recessive or X-linked.
    • Pancytopenias - due to oblieration of the marrow space.
    • Fractures.
    • Radiologic diagnosis.
  • Gross
    • Marbled appearance.
    • Thickening with obliteration of the marrow space.
    • Patchy (brown) surface due to vascularization/extramedullary hematopoiesis.
  • Microscopic
    • Abundant irregular (pink) bony trabeculae with layers of (blue-gray) cartilage.

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26 yo M w/ gastric wall mass

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Synovial Sarcoma

  • Day of:
  • Herringbone pattern w/ spindled, bland, cigar shaped cells
  • GIST morphology fits but IHC doesn't (should be DOG-1 +)
  • Ddx:
    • Lyomyoma
    • Desmoid tumour
    • Neurofibroma
    • MPNST
    • GIST
    • Schwannoma
    • Synovial sarcoma
  • Additional IHC to help support: TLE-1
  • Cytogenetics: t(X;18), SYT/SSXY/SSX2
  • Common in adolescent age group
  • Biphasic/monophasic types
  • Comes in three (histologic) flavours:
    1. Spindle cell sarcoma with features of hemangiopericytoma, i.e. staghorn vessels.
    2. Biphasic synovial sarcoma:
      • Spindle cells with features of hemangiopericytoma.
      • Epitheliod glands or nests.
    3. Primitive round cell type.
  • Features:
    • Herring bone or vesicular pattern - key feature.
    • Spindle cells.
    • +/-Glandular component - typically more pink.
    • +/-Calcification - uncommon.
    • Extensive calcification = better prognosis.
  • DDx:
    • MPNST.
      • Can be difficult.

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29 yo M w/ 20cm R pelvic mass

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  • Day of:
    • Lots of blood, fibrosis
    • RBCs extravasated
    • Lots of large, dilated vascular spaces and increased small vessels
    • Infiltration growth pattern
    • Cells appear pleomorphic, spindled and hyperchromatic; no prominent nucleoli
    • Ddx:
      • Kaposi's
        • IHC for HHV8
    • Stains:
      • vascular:
        • CD34
        • CD31
      • D240 (podoplanin)
      • ERG-1
  • Spindle cell lesion.
    • Occasionally an epithelioid lesion.
  • Very many small capillaries of irregular shape lined with:
    • Pleomorphic nuclei - important.
      • May have hobnail morphology.
    • Usually "red" at low power - due to many RBCs - important.
  • Mitoses.
  • Cytoplasmic vacuoles.
    • Cells trying to form lumina - embryologic.
  • Notes:
    • Epithelioid variant (with abundant cytoplasm & sheeting architecture) may resemble melanoma or hepatocellular carcinoma.
  • DDx:
    • Atypical vascular lesion.
    • Kaposi sarcoma.
    • Anastomosing hemangioma - especiallly in the kidney.
    • Poorly differentiated carcinoma.
    • Other vascular tumours.

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58yo M w/ 15cm R renal pole mass

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Dedifferentiated Liposarcoma

  • Malignant, generally nonlipogenic sarcoma of variable histologic grade often arising in association with identifiable component of atypical lipomatous tumor (ALT)/well-differentiated liposarcoma (WDLPS)

  • Macroscopic
    • Well-demarcated, large mass with variable cut surface
    • Important to sample thoroughly
  • Microscopic
    • Classic appearance shows abrupt or gradual transition from ALT/WDLPS to nonlipogenic, cellular sarcoma
    • Nonlipogenic component shows broad morphologic spectrum (often high grade)
    • Mitotic rate > 5 per 10 HPF
  • Ancillary Tests
    • Diffuse nuclear MDM2(+) and CDK4(+)
    • Molecular: Overexpression of MDM2
  • Top Differential Diagnoses
    • Undifferentiated pleomorphic sarcoma
    • Myxofibrosarcoma
    • Pleomorphic liposarcoma

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