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Flashcards in Pathology MSK tumors Deck (12):
1

Lipoma

-Well circumscribed, encapsulated adipose tissue w/o any areas of necrosis or hemorrhage (slow growing and painless)
-Cells look the same as normal adipose tissue, only difference is the fibrous capsule
-One variation: angiolipoma, these have variably-sized blood vessels mixed throughout the tumor
-These are benign lesions, most common soft tissue mass of adults

2

Liposarcoma

-Encapsulated mass that is fast growing and painless, usually has central area of necrosis
-Often is nodular and can have irregular margins
-Histologically can see lipoblasts (dividing adipose cells w/ hyperchromatic nuclei, key finding) in high numbers, evidence of malignancy
-Lipoblasts are variable in size and abnormal looking (strangely shaped and sized)
-Another key finding is plexiform blood cells (capillary anastamoses) and a high degree vascularization
-Found usually in retropreitoneum and deep soft tissue of proximal extremities
-Malignant lesions, very rare in children

3

Nodular faciitis

-Develops over a few months at the site of an injury (usually forearm), often in young adults
-Is semi-encapsulated, irregularly shaped
-Histologically there is spindle-cell growth, indicating fibroblasts
-At high power can see many fibroblasts, vascular proliferation and lymphocytes
-This is a benign process, reactive to the injury
-Malignant lesions from this process generally are slower growing than a few months

4

Fibrosarcoma

-Circumscribed mass, may contain some calcification
-Has ill-defined septae and capsule, which can be eroding or infiltrating adjacent bone
-Lesion often occurs in the thigh and around the knee (adult) or in muscles of distal limbs (infantile)
-Pleomorphic cell population including fibroblasts (secreting collagen), plumper cells (have vacuolated cytoplasm), and occasional giant cells
-Abnormal mitotic figures can be seen, angulated densely interlacing bundles of fibroblasts (herring-bone pattern)
-This pleomorphic fibrosarcoma is malignant and has a poor prognosis

5

Rhabdomyosarcoma

-Usually in children under 20, diagnostic cell type is the rhabdomyoblast
-Rhabdomyoblasts look like small blue round cells w/ eccentric abundant eosinophilic cytoplasm
-There can also be elongated cells that appear strap-shaped (strap cells: very long and thin). Presence of strap cells indicates a more differentiated and thus less severe disease
-Is a round blue cell tumor, see basophilic cells w/ hyperchromatic nuclei which are differentiated rhabdomyoblasts. These indicate a less differentiated and thus more severe disease
-t(2;13) associated, myoD1/myogenin positive
-These are malignant tumors and prognosis is poor

6

Osteoid osteoma

-Pts present w/ severe focal bone pain that worsens at night and w/ activities but is greatly relieved w/ aspirin (pain due to prostaglandin E, which aspirin inhibits production of)
-Usually appears before age 20 (usually boys but bimodal age distribution), often in LE
-On Xray there is a gray oval mass (nidus: lucent middle) surrounded by dense reactive bone
-The nidus is the tumor, which has disorganized interconnected trabeculae w/ high osteoblastic activity and abundant osteoid in some areas but all of it is highly vascularized
-The nidus can be seen expanding into the bone causing the reactive process in adjacent bone
-These are benign neoplasms of osteocytes/osteoblasts

7

Osteosarcoma

-Usually has metaphyseal origins and infiltrates into surrounding soft tissue (mostly affects men and knees/long bones)
-Bimodal incidence (older ppl usually due to sequellae of paget's disease)
-Associated w/ mutations in Rb, p53 genes
-Serum alk phos levels increased
-Can see malignant osteoblasts w/ little cytoplasm and large, hyper chromatic pleomorphic nuclei surrounded w/ osteoid (non-mineralized)
-Lesions are usually much larger than osteoid osteoma
-Malignant tumors

8

Osteochrondroma

-Usually in young adults (mostly boys), occurs at site after injury due to defect in growth plate particularly around knee
-Has smooth but nodular surface, w/ cartilaginous cap overlying cancellous bone (bone is highly vascularized)
-Histologically there are normal, uniform chondrocytes from the cap
-Lesion is made of both bone and cartilage, typically occurs at long bones, often around the knee
-Is a benign process

9

Ewing sarcoma 1

-Slowly growing bone mass, that is expansive and destructive (causes typical B symptoms). Mostly found in children, boys (malignant and rare)
-Causes pain and prominent periosteal reaction, is a round blue cell tumor
-Neoplasm arises form bone and extends into soft tissue, is made of friable soft tissue w/ areas of hemorrhage and necrosis

10

Ewing sarcoma 2

-There is infiltration of the medullary space by many uniform, small, round blue cells (neuroectoderm-derived)
-This lesion destroys bone but doesn't produce osteoid, often in the diaphyses of long bones
-The cells have indistinct boundaries and hyperchromatic nuclei, looks similar to lymphomas
-These lesions are positive for FLI1, the result of a t(11;22) translocation (fusion of EWS w/ FLI1)

11

Pleiomorphic undifferentiated sarcoma (PUS)

-Can be found in retroperitoneum/deep soft tissues
-Most often affects men >60 yo, is Dx of exclusion where other fibrohistiocyte lesions are ruled out (fibrosarcoma, fibromatosis, ect)
-Rarely can present as a bone lesion
-Presents as an enlarging painful mass in proximal extremity muscles or retroperitoneum, necrosis is typical
-Histologically see plump, pleomorphic large round spindle cells arranged in whirling pattern
-Can see giant cells and some inflammation, positive for vimentin
-Are malignant, and thus there isn't much ECM b/c its filled w/ cells

12

Desmoid tumor (deep-seated fibromatosis)

-Borders btwn non-aggressive tumors and low-grade fibrosarcomas, usually in teens-thirties
-Deep intramuscular or retroperitoneal mass that invades but doesn't metastasize
-Micro: plump long sweeping fascicles of fibroblasts infiltrating adjacent tissue
-Cells less pleomorphic than PUS, look more like fibrosarcoma cells
-Fewer cells than PUS or fibrosarcoma b/c is not malignant