Improvements in imaging technologies have made the process of defining the extent of bone tumors like osteosarcomas increasingly accurate.
But while it’s easier than ever to say, “The tumor starts here and ends here,” when removing a bone tumor surgically, surgeons still need to take a moment during the operation to check the edges (or “margins”) of the removed and remaining bone for any signs of remaining tumor, a step called intraoperative assessment.
“You need to make sure the tumor has been completely removed and a safe amount of normal tissue remains as a buffer,” says Sara Vargas, MD, director of patient safety and quality in Boston Children’s Hospital’s Department of Pathology. “Achieving a margin that is free of tumor reduces a patient’s long-term risk of local tumor recurrence.”
During surgery, there are two ways to do the assessment, each method providing a check on the other: gross split specimen inspection and frozen section inspection.
The two methods, which are often done either simultaneously or in tandem during surgery, are quite different. In frozen section, a pathologist takes a sample of marrow from the remaining bone, freezes it, slices it thinly and checks under the microscope for the presence of tumor cells. For gross split, the removed section of bone is cut in half and assessed directly by a pathologist and the surgeon.
If the two assessments show no tumor at the margins, then the surgeon can start the reconstruction phase of the procedure. If tumor tissue remains at the margins, then the surgeon will likely remove additional bone and reassess before starting the reconstruction phase of the procedure.
In routine practice, though, most surgeons rely on the results of gross split when deciding whether to remove more bone. Vargas and Megan Anderson, MD, an orthopedic surgeon with the hospital’s Bone and Soft Tissue Tumor Program who specializes in bone tumor removal, wanted to know: Are both methods of assessment really necessary?
“Anything we can do to reduce a patient’s time under anesthesia is a good thing.”
“We typically either do both or just gross split,” Anderson notes. “Split sections let you see where the tumor starts and stops, and we wanted to know whether as a general rule we really could rely just on one assessment.
“Bone resection and reconstruction procedures are long, often 6 to 10 hours,” she adds, noting that a frozen section assessment takes about 20 minutes and a gross split about a half hour. “Anything we can do to reduce a patient’s time under anesthesia is a good thing.”
To answer their question, Vargas and Anderson reviewed the records of 142 children who underwent surgery at Boston Children’s for a primary bone tumor (mostly osteosarcomas) over a 14-year period. They then checked the results of frozen section and gross split assessments against the subsequent surgical decisions and the full pathology report for each child’s tumor.
As the pair reported in a recent paper in the journal Clinical Orthopedics and Related Research, the gross split and frozen sections agreed 92 percent of the time. In the few cases where they didn’t agree, the surgeon decided whether to remove additional bone on the basis of the gross split analysis, discarding the results of the frozen section.
The full pathology reports on the patients confirmed that each patient had clear margins; the surgeons had gotten the entire tumor out before starting to reconstruct the affected limb.
“The findings indicate that gross split is enough when it comes to routine practice,” Anderson says, adding that assessment by gross split specimen alone is now standard practice for the 20 to 30 bone tumor resections she and her colleague Mark Gebhardt, MD, carry out every year at Boston Children’s. “Potentially, that is 20 minutes of operating room time that we can eliminate from these procedures.”
In addition to the benefit to the patient, there is a cost benefit to carrying out a single assessment.
“It requires more work, but a gross split assessment is less expensive than a frozen section assessment,” Vargas explains. “Carrying out just the gross split assessment alone should then help reduce the charges associated with a patient’s procedure.”
Anderson cautions that the results are not universally applicable. “Not all hospitals have the facilities or subspecialized pathologists you need in order to conduct a gross split assessment,” she notes. “The results reflect our own experiences here at Boston Children’s, which may differ from those of other centers.
“At the very least,” she continues, “our results have prompted a discussion within the orthopedic surgical community about what way is the best way to carry out intraoperative consultations during bone tumor resections, something for which there are no guidelines or literature.”