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A Review of Pathology Claims from 1998–2003

The clinically significant diagnostic (cognitive) error rate in surgical pathology reported in the literature varies from 0.26 percent to 1.2 percent when uncovered by prospective review of all cases or discovered when a random sample of cases is reviewed.

A “blinded” review of 5,000 sequential biopsies revealed a clinically significant error rate of just 0.08 percent. Thus, surgical pathology has a relatively low diagnostic error rate, which is somewhat surprising considering that pathologists apply a confusing array of diagnostic criteria that are both evidence based and empirical to a relatively small number of difficult cases randomly admixed with a large number of “routine” cases—and often with incomplete or misleading clinical information.

There are many ways to define “error” in surgical pathology, e.g., cognitive vs. operational error, clinically significant vs. academic error (differences in classification, nomenclature, grading), error as defined by prospective vs. retrospective review, or error as defined by “expert” second opinion, intradepartmental review, or interinstitutional review. Measurement is further compromised by hindsight bias (knowledge of outcome) and the problem of interobserver diagnostic reproducibility. Our judicial system, however, defines error as injury resulting from negligence. Negligence is defined by expert testimony as medical practice that falls below the standard of care. Standard of care is the professional behavior expected of a prudent, careful, and informed physician; it is a national standard, not a “community” standard, and is increasingly difficult to differentiate from “best practice.” Pathologists may be held to a higher standard of care. We are viewed as “the doctors’ doctor,” rendering a “final diagnosis” that is achieved through an objective scientific observation of cells and tissues—in contrast to the “art” and subjectivity of clinical decision-making. Finally, injury must be the consequence of negligent professional behavior: negligence must be the proximate cause of injury.

If a patient perceives that he or she has been injured as a consequence of a pathologist’s misdiagnosis (resulting in an inappropriate treatment or a delay in diagnosis), he or she may file a malpractice claim. A review of malpractice claims is yet another way of measuring error—error as defined by society and the judicial system.

Claims frequency is the number of claims reported each year per 100 insured physicians. As a specialty, pathology has low frequency. From 2000–2003, on average, a claim was filed each year against 8.3 percent of The Doctors Company’s insured pathologists. Stated differently, the “average” pathologist had a claim every 12 years. Claims severity is the average indemnity plus loss-associated expense paid per closed claim. Pathology has high severity, because many pathology claims result from the failure to diagnose cancer. From 2000–2003, the average claim severity for all of our pathology claims was $453,201—whereas melanoma claims severity was $757,146 (95 percent involved a false-negative diagnosis); Pap smear claims severity was $686,599 (98 percent were false negatives); and breast cancer claims severity was $203,192 (false negatives and false positives were evenly divided).

Pathology claims from 1995 through 1997 were previously analyzed in “A Review of Pathology Claims from 1995–1997.” In order to see if new repetitive patterns of specimen type or diagnostic category were emerging, 378 additional pathology claims from 1998 through 2003 were reviewed. When nuisance claims (9.5 percent of total) and claims involving autopsies (2 percent of total) were excluded, 335 claims remained. These are categorized in the table on the following page.

Of these claims, 14.5 percent are surgical pathology claims representing “random errors” that show no particular pattern relating to specimen type, diagnostic category, or diagnostic error. Within this Miscellaneous Surgical Pathology category:

• Five claims resulted from missed infectious agents (Coccidioides immitus, TB, Aspergillus, leprosy, and chorioamnionitis).
• One claim involved “missed” brain tissue admixed with sinus contents, indicating surgical perforation of the sinus.

The remaining 85.5 percent of pathology claims fell into repetitive patterns of specimen type or diagnostic category—suggesting “systematic errors.”

 
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Overall, 63 percent of these claims involved the false-negative diagnosis of cancer, and 22 percent involved the false-positive diagnosis of cancer. Over half of the claims (57 percent) involved melanoma, breast specimens, Pap smears, gyn specimens, and operational errors. Significant observations regarding these claims include:

• Of the 42 melanoma false-negative claims, 29 percent were melanomas misdiagnosed as Spitz nevi (three), “dysplastic” nevi (three), spindle cell squamous carcinoma (three), and atypical fibroxanthoma (one); two were unrecognized desmoplastic melanomas. The misdiagnosis of melanoma is a continuing problem for pathologists and has become the single most common reason for filing a claim against a pathologist.
• Of the 42 breast biopsies, 79 percent were excisional biopsies, and 21 percent were cutting needle biopsies. Four involved the misdiagnosis of ductal carcinoma in situ (DCIS), one involved lobular carcinoma in situ (LCIS), and two involved lymph node metastases that were missed. While breast biopsy claims are a close second to melanoma, when combined with breast fine needle aspiration (FNA) and breast frozen section claims, breast specimens account for 15.5 percent of all claims and are the most common cause of pathology malpractice claims. Breast biopsy claims are almost evenly divided between false negatives and false positives.
  
  In a review of claims from 1995–1997, the majority of breast FNA claims were false negatives resulting from sampling error—typically in a woman with a palpable breast mass subsequently diagnosed as carcinoma. False-positive breast FNAs were usually interpretation errors—typically an FNA diagnosis of carcinoma made on a fibroadenoma. The current data show a decrease in the number of breast FNA claims. Whether this decrease represents improved practice performance or an increased preference for cutting needle biopsy cannot be determined.
  
  
• Of the 31 gynecologic pathology claims, 42 percent (13 claims) involved misdiagnosed ovarian tumors. Eleven of these were false-negative diagnoses of malignancy (85 percent), and two were false positives (6 percent). False-negative diagnoses included the misdiagnosis of serous carcinoma as a serous tumor of low malignant potential (LMP), of serous tumors of LMP as serous cystadenoma, of metastatic mucinous carcinoma as mucinous cystadenoma, of mucinous cystadenocarcinoma as a mucinous tumor of LMP, of immature teratoma as mature teratoma, and of small cell carcinoma of hypercalcemia type as dysgerminoma.
• Twenty-two of the total 335 claims (6.5 percent) involved specimen “operational errors”:
• Thirteen claims (59 percent) involved specimen “mix-ups” resulting in one patient getting an incorrect malignant diagnosis and another getting an incorrect benign diagnosis. Eighty-five percent (11) of these claims involved breast (seven) or prostate (four) needle biopsies; one was a lung biopsy; and one was a gastric biopsy.
• Three claims were for lost breast needle biopsies.
• Three involved “floaters” (prostate, colon, lymph node fragments).
• Two involved mislabeled biopsy sites.
• One was a transcription error (failure to type “no” in front of “malignant cells identified”).
• Of the 12 claims involving the false-negative diagnosis of sarcoma, four (33 percent) were monophasic synovial sarcomas.
• Of the eight claims involving the false-negative diagnosis of lymphoma, 63 percent (five) were extra-nodal lymphomas. Of the six claims involving a false-positive diagnosis of lymphoma, two were extra-nodal reactive hyperplasias, and one was a melanoma metastatic to lymph node. The extranodal sites included breast, stomach, bone, nasopharynx, rectum, and parotid. Overall, 50 percent of lymphoma claims involved extra-nodal lymphomas or reactive hyperplasias.
• Of the gastric biopsy claims, four of the five false negatives involved signet ring carcinoma, as did one of the seven false positives.
• Fifteen of the total 335 claims involved frozen section misdiagnoses (4.5 percent), and one-third of these were breast frozen sections.
• Seven of the total 335 claims (2 percent) involved false-negative diagnoses of malignant salivary gland tumors (most were misdiagnosed as pleomorphic adenoma).
• Five of the total 335 claims (1.5 percent) involved the appendix: two of these were missed mucinous cystadenocarcinomas, while one involved mistaking a colonic diverticulum for the appendix.
• There has been a significant decrease in miscellaneous FNA claims—which probably represents greater practice experience with this diagnostic technique.
• Claims involving failure to diagnose carcinoma in situ (CIS) of the urinary bladder and claims involving cervical lymph nodes containing metastatic squamous carcinoma misdiagnosed as branchial cleft cyst continue.
• Claims involving prostate needle biopsy remain relatively infrequent. Two-thirds of these claims involve the failure to diagnose carcinoma whereas in a previous review, more than two-thirds of claims involved a false-positive diagnosis of carcinoma. This shift may reflect pathologists’ greater familiarity with the mimics of carcinoma (partial atrophy, adenosis, etc.).
• Claims for false-negative Pap smears have decreased from 17 percent of total claims in 1995–1997 to 12.5 percent and are now third in frequency behind melanoma and breast specimens.

Discussion

When the repetitive patterns of specimen type and diagnostic error identified in claims filed from 1998 through 2003 are compared to those found in the claims filed from 1995 through 1997, both new patterns and continuing trends can be identified:

• Claims involving the misdiagnosis of melanoma have increased from 11 percent to 13 percent of total claims and have become the single most common reason for filing a claim against a pathologist. Twenty-nine percent of the false-negative claims were melanomas misdiagnosed as Spitz nevi, “dysplastic” nevi, spindle cell squamous carcinoma, and atypical fibroxanthoma; several were unrecognized desmoplastic melanomas. The misdiagnosis of melanoma is a continuing problem for pathologists. For an in-depth discussion, see our article “Melanoma Expert Panel Report.”
• While claims involving breast biopsy are now a close second to melanoma claims, when combined with breast FNA and breast frozen section claims, “breast specimens” account for 15.5 percent of all claims and are the most common cause of pathology malpractice claims. Breast biopsy claims are almost evenly divided between false negatives and false positives, and 21 percent of all breast biopsy claims involved large core (cutting) needle biopsies. There are no significant trends, except for a decrease in breast FNA claims. Whether this represents improved practice performance or an increased preference for cutting needle biopsy cannot be determined.
• Diagnostic errors involving CIS of the lower urinary tract can be minimized by becoming familiar with the spectrum of low-grade and high-grade intraurothelial neoplasia; specifically looking for these lesions when examining bladder biopsies—whether or not there is an associated urothelial carcinoma; and in transurethral prostatic resection (TURP) specimens, looking carefully at tissue from the urethra and periurethral prostatic ducts for evidence of CIS—especially if there is a history of bladder carcinoma or CIS.

Transitional CIS of the urinary bladder (highgrade intraurothelial neoplasia) is present in most patients who have invasive urothelial carcinoma, and it is in this setting that CIS is usually diagnosed. Less frequently, CIS presents with symptoms of chronic cystitis in a patient without an associated urothelial carcinoma, and in this context CIS is often not recognized.

Transitional CIS is typically multicentric. CIS does not always occupy the full thickness of the bladder mucosa, and the Consensus Classification of Urothelial Neoplasms states that CIS includes lesions previously called severe dysplasia. CIS is easily dislodged by instrumentation and biopsy—so it is important to carefully examine areas of denuded mucosa since only a few cells may cling to the surface (clinging variant).

Up to 20 percent of cases of CIS extend from the bladder into the prostatic urethra and periurethral prostatic ducts. Therefore, in patients with bladder CIS, urologists may biopsy the prostatic urethra and suburethral prostate to stage the lesion. It is important to identify urethral and prostatic involvement, because conservative treatment of bladder CIS involves intravesicle chemotherapy or immunotherapy, which acts through direct contact with the lesion. Since this therapy will not directly access urethral or prostatic CIS, many urologists perform prostatectomy when CIS is identified in these locations. Since CIS is looked for when staging biopsy of the urethra and prostate are performed, it will usually be identified. However, it is apt to be overlooked in a TURP specimen unless the pathologist knows there is a history of bladder CIS or urothelial carcinoma.

Urothelial dysplasia (low-grade intraurothelial neoplasia) includes both mild and moderate dysplasia; severe dysplasia is now included in the spectrum of CIS. Dysplasia is usually diagnosed in bladders harboring urothelial carcinoma or CIS. Little is known about its natural history, although one report suggests that as many as 19 percent of cases may progress to either CIS or urothelial carcinoma.

• The misdiagnosis of metastatic well-differentiated squamous carcinoma as branchial cleft cyst is an ongoing problem. Patients are typically relatively young males (ages 32 to 45) in an age group where “cancer” is not the first diagnostic consideration. Branchial cleft cyst is often the clinical diagnosis, contributing to the pathologist’s mindset when examining the case. The squamous carcinoma is usually well differentiated and cystic. At the time of misdiagnosis, there is usually no known primary carcinoma—contributing to the failure to consider metastatic squamous carcinoma. In most cases, an occult primary in the oropharynx or nasopharynx is subsequently found.

Diagnostic errors involving branchial cleft cyst can be minimized by: 1) not making a diagnosis of branchial cyst without first considering the possibility of metastatic cystic squamous carcinoma—regardless of the patient’s age and clinical diagnosis; 2) looking carefully for cytologic atypia in the lining squamous epithelium—and, if present, alerting the clinician to the need for a thorough workup to exclude an occult primary in the head or neck; and 3) hesitating to make an FNA diagnosis of “consistent with branchial cyst” based on a few bland squamous cells in sparsely cellular fluid aspirated from a neck mass. It may be more appropriate to make a diagnosis of “nondiagnostic due to sparse cellularity”—which leads to biopsy.

An effective quality assurance program is essential to any strategy for minimizing diagnostic (cognitive) error. The low clinically significant diagnostic error rate (circa 1.2 percent or less) probably does not justify prospective review of all diagnoses. However, intradepartmental review of difficult or unusual cases (melanomas, lymphomas, sarcomas, bone tumors), new diagnostic procedures (breast needle biopsy), problem-prone pathologists, “new” pathologists, and provisional malignant or atypical or suspicious diagnoses is appropriate. When this “second intradepartmental opinion” is concordant with the provisional diagnosis, it should be documented in the final report or on the file copy. If the review is nonconcordant, the case should be reviewed by another pathologist or sent for consultation to an expert. A quality assurance program is easy to implement, effective, and reassuring to clinicians.

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