Patients with malignant pleural mesothelioma (MPM) often undergo multiple diagnostic and therapeutic pleural procedures.1 Needle tract metastasis (NTM) from seeding of mesothelioma cells along the pleural intervention tract is a well-recognized complication. Conventionally, the diagnosis of NTM, and their treatment with radiotherapy, is based on clinical judgment only. Histologic proof of malignancy of the subcutaneous lesions is not required even for entry to any of the published randomized trials on NTM.2–4
We describe 2 mesothelioma patients who had “false” NTM at their pleural puncture sites and highlight the need to keep a high index of suspicion for benign causes of such lesions.
A 74-year-old retired asbestos miner presented with a right pleural effusion. Thoracoscopic biopsy confirmed MPM. He underwent talc pleurodesis but his effusion recurred 3 months later. An indwelling pleural catheter (IPC) was inserted and provided symptomatic benefits.
Four months after IPC insertion, he presented with fever and dyspnea. Pleural fluid culture yielded Staphylococcus aureus. He was successfully treated with intravenous flucloxacillin and intrapleural tissue plasminogen activator and deoxyribonuclease.
The infection induced a pleurodesis and he had no fluid recurrence over 7 weeks. The IPC was removed electively, at which time a new subcutaneous lesion was found at the pleural insertion site of the catheter (Fig. 1). The nodule was firm and tender, and clinically suspicious of a tract metastasis. Referral for irradiation was considered.
However, a core biopsy of the lesion showed no evidence of mesothelioma but inflamed granulation tissue with abundant neutrophils, focal necrosis, and microabscesses (Fig. 2). Computed tomography also found no evidence of NTM along the IPC tract. The nodule resolved spontaneously within a month and had not recurred after 7 months of follow-up.
A 74-year-old man presented with a right pleural effusion. Video-assisted thoracoscopic biopsies confirmed an epithelioid mesothelioma. He received a talc poudrage and prophylactic radiotherapy to the port sites.
His effusion recurred 4 months later (Fig. 3) and he was referred to our clinic. An IPC was inserted but his insertion sites healed poorly (presumably related to prior radiotherapy and poorly controlled diabetes). He had persistent fluid leak around the catheter tract, which settled after 4 weeks.
A new subcutaneous nodule (1 to 2 cm in size, firm, and nontender) was found near the initial pleural puncture site for the IPC insertion 1 month later, suspicious of an NTM. A fine-needle aspiration was performed but the nodule “deflated” upon aspiration (Fig. 4) surrounded by turbid discharge. The cytology showed no mesothelioma but acute inflammatory cells (Fig. 5).
The concurrent pleural fluid drained from his IPC appeared turbid and grew S. aureus. The patient was treated with antibiotics and the lesion did not recur at follow-up after 4 months.
We described 2 MPM patients who developed subcutaneous lesions of nonmalignant etiologies mimicking NTM.
The incidence of NTM varied from 2% to 50% in literature reports. The risk for NTM related directly to the size of pleural punctures (highest with thoracoscopy/thoracostomy).5 The pathogenesis remains unclear. The role of prophylactic radiotherapy is debated as 3 small randomized trials showed conflicting results. The indwelling nature of IPCs presents a persistent risk higher than one-off interventional procedures. In a small study specifically addressing the issue, 6.7% of IPC patients developed tract metastases.6 Another review of 250 IPCs, however, only showed an incidence of 0.4%7 and a literature review showed an incidence of 3.4%.8
There are no diagnostic criteria for NTM, which is based solely on clinical judgment of new subcutaneous lesions developed over a pleural puncture site. Some clinicians only irradiate NTMs when painful; others advocate early treatment when lesions are small and before pain ensues.9 Clinical guidelines have not advocated histologic confirmation, which is rarely sought in “real world” practice. This may be related to the fear that biopsies will create further needle tract spread. Also, the disease is generally sensitive to radiotherapy, which is relatively safe and effective. Hence, clinicians often have a low threshold of initiating treatment without definitive histologic proof.
Our cases reminded clinicians of alternative (benign) explanations to NTM. The incidence of “pseudo-NTM” is unknown. Had biopsies not been performed in these 2 patients, they would have been treated with radiotherapy and considered “responders.”
Both patients had S. aureus pleural infections before the inflammatory nodules developed. Whether having an IPC and/or pleural infection raises the risks for these “pseudo-NTM” is unknown. Both nodules were small and the nonmalignant nature may have become clear had we observed the lesions over time. Nonetheless, bedside aspiration was a simple procedure and allowed prompt exclusion of malignant deposits. Clinicians should have a low threshold to perform bedside aspiration especially when there are suggestions of potential alternative etiologies, such as concurrent cellulitis around the IPC site.
These cases highlighted that benign inflammatory nodules can develop over pleural puncture sites in mesothelioma patients. Future studies should aim to clarify the clinical features that favor genuine malignant tract deposits. If in doubt, percutaneous sampling can be helpful.
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Keywords:© 2014 by Lippincott Williams & Wilkins.
mesothelioma; metastasis; biopsy