Surgical Pathology Web Conference
Case 1
Clinical History:
A 65-year-old man had pain in his knee for several years. A plain radiograph
demonstrated a defused radiodensity in the distal femur. The radiodensity was due to
coarsened trabecular bone.
Differential Diagnosis:
A. Metastatic prostate carcinoma
B. Paget’s disease
C. Osteomyelitis
Diagnosis: B
Paget’s disease
This is an example of late phase Paget’s disease with sclerotic bone, The principle
histologic finding is an increase in remodeling line that form a mosaic pattern.
This increase is due to the exaggerated and chaotic bone-remodeling characteristic
of Paget’s disease. In addition, osteoclastic activity is very prominent. Many osteoclasts
are gigantic.
Although metastatic carcinoma is an important consideration in any bone lesion in
this age group, the absence of epithelial cells rules out this diagnosis. Often, keratin stains
must be performed to exclude the presence of hidden epithelial cells. Prostate cancer
causes a similar increase in bone density. However, the mosaic pattern of remodeling
lines is not present in metastatic prostate cancer. In addition, almost all patients with
metastatic prostate cancer will have an elevated PSA. By contrast, patients with Paget’s
disease almost always have an elevated alkaline phosphatase
The diagnosis is not osteomyelitis. Although osteornyelitis may produce marrow
fibrosis and increased bone density similar to Paget’s disease, the mosaic pattern of
remodeling is not present in osteomyelitis. In addition, osteomyelitis does not show giant
osteoclasts.
Case 2
Clinical History:
A 70-year-old woman had pain in her arm. A radiograph showed an aggressive
lytic lesion involving much of her proximal radius.
Differential Diagnosis:
A. Lymphoma
B. Metastatic carcinoma
C. Multiple myeloma
D. Osteomyelitis
Diagnosis: C
Multiple myeloma
Multiple myeloma almost always produces lytic lesions in bone. In most cases,
there are multiple lesions. However, occasionally a solitary myeloma may present as a
single lytic lesion with no other sites of involvement. Only a staging study can
differentiate multiple myeloma from solitary myeloma. Multiple myeloma consists of
sheets of plasma cells. Sometimes they may be so poorly differentiated as to their
plasmacytic nature. However, a CD138 stain should be performed on any round cell
tumors. CD 138 is specific for plasma cells. To corroborate the neoplastic nature of these
cells, a kappa and lambda immunostain should be performed. Myeloma will be
monoclonal and either for only kappa or only lambda.
Although lymphoma of bone occurs in this age group and shows sheets of
rounded cells, the plasmacytoid nature is usually not present. Furthermore, a CD 138
stain will be negative. Usually, primary lymphomas of bone are B-cell lymphomas and
stain strongly with a CD2O stain.
The lesion is not metastatic carcinoma because epithelial cells are not present. In
this age group metastatic carcinoma should always be a strong consideration. Often, a
keratin stain must be performed to absolutely exclude the diagnosis of metastatic
carcinoma.
Although osteomyelitis may demonstrate many plasma cells, this case is not
osteomyelitis because the plasma cells will be monoclonal. In addition, chronic
osteomyelitis produces a radiodense pattern unlike this case that shows an aggressive
radiolytic pattern.
Case 3
Clinical History:
A 20-year-old man had a swollen big toe. One-year prior he had dropped a brick
on his toe. The radiograph demonstrated a bony protrusion arising from the dorsal aspect
of the great toe distal phalange.
Differential Diagnoses:
A. Subungual exostosis
B. Osteochondroma
C. Myositis ossificans
D Parosteal osteosarcoma
Diagnosis: A subungual exostosis
The radiographic image is critical for the diagnosis in this case. The radiographic
pattern is diagnostic of a subungual exostosis. This disease is a bony growth underneath
the nail, usually as a result of trauma. There is woven bone proliferation in the soft tissues
in periosteum on the dorsal aspect of the distal phalange.
There is a distinct zonal pattern of bone formation with the more immature bone
closer to the nail. Eventually the nail can be pushed up at a right angle to the toe.
The lesion is not an osteochondroma because osteochondromas are developmental
lesions and do not occur in the phalanges. A rare exception is in cases of hereditary
multiple exostosis. Osteochondromas usually occur in the long bones and have a very
distinctive cartilage cap.
Although myositis ossificans is a reasonable alternative consideration, this lesion
is not officially myositis ossificans because no muscle is present. Indeed myositis
ossificans is a reactive proliferation of woven bone, as is this case. However, in this
location, the lesion is known as a subungual exostosis.
The zonal pattern and the lack of atypia in the stroma between the new bone
formations exclude the possibility of a parosteal osteosarcoma. Moreover parosteal
osteosarcomas in the phalanges are extremely rare.
Case 4
Clinical History:
A 30-year-old man had pain in his lower leg. A radiograph demonstrated a lytic
expansile lesion in his distal tibia. An MRI showed multiple fluid-fluid levels.
Differential Diagnoses:
A. Telangiectactic osteosarcoma
B. Giant Cell Tumor
C. Aneurysmal bone cyst
Diagnosis: C Aneurysmal bone cyst
The MRI pattern in this case is characteristic of aneurysmal bone cyst. The fluidfluid levels visible on a T2 MRI represent blood filled lakes present in the lesion. These
blood filled lakes are the hallmark of an aneurysmal bone cyst. The stroma separating
these blood filled cavities consists of fibrous tissue with numerous multinucleated giant
cells and reactive bone.
Although telangiectatic osteosarcomas can have a similar radiographic pattern,
especially on the MRI, the absence of frank sarcomatous strorna eliminates the
possibilityof osteosarcoma. Telangiectactic osteosareomas have blood filled lakes similar
to aneurysmal bone cysts, but they are filled with sheets of large pleomorphic, atypical
osteoblasts.
The lesion is not a giant cell tumor. Although giant cells are prominent in
aneurysmal bone cysts, the metaphyseal location of this lesion excludes the possibility of
this being a giant cell tumor that always involves the epiphyseal end of a long bone.
Aneurysmal bone cysts may be a component of giant cell tumors, but this case represents
a pure aneurysmal bone cyst.
Case 5
Clinical History:
A 20-year-old man had pain in his shoulder for 6 months. The radiograph
demonstrated a poorly defined radiolytic and radiodense lesion with cortical destruction.
Differential Diagnoses:
A. Osteosarcoma
B. Osteoblastoma
C. Malignant fibrous histiocytoma
D Parosteal osteosarcoma
Diagnosis: A
Osteosarcoma
Osteosarcoma is the most common primary malignant bone tumor and usually
occurs in young adults and adolescents, as in this case. Histologically, sheets of atypical
and pleomorphic sarcoma cells make pink seams of osteoid. This feature designates these
cells as osteoblasts and the lesion, therefore, as an osteosarcoma. The radiograph in this
case is diagnostic.
The lesion is not an osteoblastoma. Osteoblastomas are well-defined lytic lesions.
They manufacture abundant osteoid, but they are not composed of atypical and
pleomorphic osteoblasts.
The lesion is not a malignant fibrous histiocytoma because of the extensive
osteoid formation. Some osteoid osteogenic sarcomas may have a predominant histologic
pattern of malignant fibrous histiocytoma, the presence of osteoid formation requires the
diagnosis of osteosarcoma.
The lesion is not a parosteal osteosarcoma because parosteal osteosarcoma is
entirely a surface lesion. This case involves the medullary canal of bone. Occasionally, a
CT scan must be performed to see if the medually canal is involved when there is
extensive soft tissue involvement with osteosarcoma. Moreover parosteal osteosarcomas
are low-grade sarcomas and do not show severe pleomorphism.
Case 6
Clinical History:
A 45-year old man had pain in both his legs. Radiographs demonstrated defuse
radiodensity in a zonal pattern that involved both femurs. In addition, this gentleman had
defused radiodensities involving many other long bones. A biopsy showed numerous
histiocytic-like cells, and an S100 stain was negative.
Differential Diagnosis:
A. Osteomyelitis
B. Langerhans’ cell histiocytosis
C. Erdheim-Chester disease
D. Rosai-Dorfman disease
Diagnosis: C Erdheim-Chester disease
Erdheim-Chester disease is a systemic proliferation of histiocytes that involve
many bones of the skeleton. In any one bone, a radiographic pattern is similar to chronic
osteomyelitis. However, unlike chronic osteomyelitis, many bones in the skeleton are
involved. In addition, wound cultures in Erdheim-Chester disease are negative.
The lesion is not osteomyelitis because of the multiple bones involved and
because cultures were negative. Otherwise, the histologic pattern of any one lesion (as
well as the radiographic pattern) could be highly suggestive of osteomyelitis.
The lesion is not Langerhans’ cell histiocytosis because the S100 stain is negative.
Langerhans’ cell histiocytosis is a histiocytic proliferation that may involve multiple
bones. However, the lesions are usually punched out and lytic, and they do not form a
pattern of irregular radiodensity as in this case.
Rosai-Dorfman disease is also a histiocytic proliferation that occasionally may
involve one or more bones. This disease usually involves lymph nodes, but has been
reported in a wide variety of visceral locations, including bone. S100 stain is positive in
Rosai-Dorfman disease, and this case could not be given that diagnosis.