Weatherly's Woes - Bone Tumors

BONE TUMORS

As a group, bone tumors are unusual because they tend to occur in boys. And not many other medical conditions can say that! The reason it affects them is that children have active growth plates. Adults have a closed epiphyseal plate, so there’s little risk for malignancy. Boys probably get bone tumors more often than girls because boys grow to be taller.

Bone tumors can present in three ways. (1) Asymptomatic tumor that’s picked up incidentally on imaging, (2) bone pain and (3) pathologic fracture. The labwork is usually normal, except for osteoblast tumors which can have a high Alk Phos.

OSTEOBLAST TUMORS

An OSTEOID OSTEOMA is a small, benign Osteoblast tumor. It likes to grow on the outside (cortex) of the diaphysis of long bones. Bone tumors hurt, and this is no exception. Since OO’s are small, the pain is usually well controlled with NSAIDs alone (this isn’t true of the bigger Osteoblast tumors). The inside of the tumor is filled with Osteoid (since osteoblasts make osteoid), and since osteoid lacks calcium, the core will look dark on an x-ray. At the border of the tumor, the Osteoid on the outside will mineralize, giving it a dense white border on x-ray. Alk phos is high.

An OSTEOBLASTOMA refers to an osteoid osteoma that is larger than 2cm. It’s more commonly found on the spine and pelvis. One of the big differences is that NSAIDs alone can’t control the bone pain. Alk phos is high.

An OSTEOSARCOMA is a cancer of Osteoblasts. It’s the most common primary bone tumor. There is a bimodal age distribution - it’s mostly teens but also some old people (with Paget Disease). Teens who’ve had radiation therapy as kids are especially at risk (a child who survived ALL, but goes on to get an Osteosarcoma). There are also some genetic conditions that predispose to Osteosarcoma, like Familial Retinoblastoma (Rb gene mutation) or Li Fraumeni Syndrome (p53 mutation). Osteosarcoma usually arises from the metaphysis (growth plate) of long bones, most commonly on the distal femur, near the knee. It can present as a painful bone mass or as a pathological fracture. As the tumor grows away from the bone, it drags the periosteum with it, creating a sloping angle (Codman’s Angle) that resembles a gentle hill on an x-ray. If the tumor breaks through the periosteum, it can have a hazy border resembling a sunburst. Histology shows scary looking cancer cells alongside pools of pink osteoid.

OSTEOCHONDROMA

Bone+cartilage tumor

An Osteochondroma is a benign bone (osteo) tumor of the growth plate, that’s topped with cartilage (chondro). These tumors often have a dramatic appearance with a large amount of growth perpendicular to the bone. Since it grew out of a physiological process (endochondral bone formation), the bone is actually kinda normal, hence it’s topped with cartilage and contiguous with the bone marrow. Note that the overlying cartilage is “out of its element” and can sometimes turn into cancer (Chondrosarcoma).

CARTILAGE TUMORS

A Chondroma is a benign cartilage tumor. It tends to occur in the medulla (bone marrow) of the hands or feet.

A Chondrosarcoma is a cancer of cartilage. It tends to occur in the medulla (bone marrow) of the pelvis or spine.

GIANT CELL TUMOR

Osteoclastoma

A Giant Cell Tumor is a weird bone tumor that defies categorization. The neoplastic cells (which are derived from Osteoblasts) express RANK-L on their surface, and we know that RANK-L activates clasts. So in this disorder, the osteoclasts are revved up, hence the presence of multinucleated giant cells (which represent really “angry” osteoclasts). This tumor initially seems like it’s all osteoclasts, which is why its nickname is an “Osteoclastoma,” but in reality this is still a neoplasm of blasts. On an x-ray, it will have a “soap bubble” appearance on a long bone. Here’s my theory of why it looks like this. The bubble expands outwards, because it’s an osteoblastic tumor at heart. But since it also activates osteoclasts, the inside of the tumor is eaten away. The Giant Cell Tumor is usually benign (98% of the time) but it has some cancerous potential (2% of the time). But it’s an unpredictable bugger, and it likes to invade local structures. This is the only tumor involving the epiphysis!

EWING SARCOMA

Cancer of bone stem cells

Ewing Sarcoma is a cancer of immature neuroectoderm cells that arise from within the bone marrow of the diaphysis of long bones. Usually occurs in boys. The immature neuroectoderm cells look very similar to lymphocytes (round blue cells with enormous nuclei), which makes the biopsy difficult to differentiate from a lymphoma or chronic osteomyelitis. Furthermore, since Ewing’s sarcoma starts in the bone marrow, there are often systemic symptoms like fever and cytopenias. To prove that it’s cancer, you need to do a biopsy and test for t(11;22). Although it’s an aggressive cancer, it responds really well to chemo.

Patrick Ewing was a famous NBA player for the New York Knicks. His number was 33 (11 + 22 = 33). His uniform was adored by the cheering crowds (crowded uniform histological appearance). Unfortunately, the Knicks franchise is run by a cancerous owner, James Dolan. Finally, fans love to buy onion rings at the concession stand (onion skinning x-ray).

Subtle periosteal onion-skinning

Crowded anaplastic bone marrow

OTHER BONE TUMORS

Potpourri

An OSTEOMA is a benign bone tumor. They usually grow on facial bones. They’re associated with Gardner Syndrome (one of the familial adenomatous polyposis diseases). That’s an important fact, because the osteomas often precede the development of colon symptoms. Knowing this fact may save a child from colon cancer! Note that there’s another cause of skull tumors -- Langerhans Cell Histiocytosis -- which you can identify based on the presence of Eosinophils.

BONE CYSTS are fluid filled bone bubbles with fibrous linings. Usually an incidental finding, but ill-placed cysts can cause a pathological fracture. They usually improve with time. Tends to occur in the metaphysis.

BONE METASTASES are more common than primary bone tumors. Metastases usually cause osteolytic (dark) lesions. Multiple myeloma is famous for this. A notable exception is prostate cancer, which tends to form osteoblastic lesions (white blobs, just like the prostate itself).

Osteoblastic (white)

Osteolytic (dark)