Causes and Risk Factors for Recurrence
Different risk factors have been correlated with the occurrence of RPA: some of them pertain to the histologic and biologic profile of the tumor, and some others are related to the surgical technique. It is believed that some features of the tumor, namely the existence of pseudopodia, multifocality, discontinuous pseudo-capsule, and hypocellular or myxoid subtype may carry a higher risk of recurrence. All these factors, indeed, are potentially associated with ill-defined margins of the lesion and, consequently, with the possibility of leaving residual disease. However, the most relevant risk factors for RPA are related to surgery: incisional biopsy of the lesion, incomplete removal or enucleation without a free tissue margin, and intraoperative pseudo-capsule violation with possible tumor spillage are all believed to concur in increasing the risk of leaving neoplastic remnants. Simple tumor spillage seems to increase the risk of recurrence by 5%, whereas incisional biopsy and enucleation can increase the risk by as much as 45%.
Diagnosis
RPA usually occurs 7–10 years after surgery, but the possibility of recurrence even after 15–20 years should not be overlooked. The diagnosis of RPA may be suggested by either clinical examination or imaging assessment (ultrasound scan [US]; ± fine needle aspiration cytology [FNAC], and magnetic resonance [MR]). Clinically, the suspect of RPA is raised by the presence of single or multiple nodules, generally asymptomatic and with variable dimensions, in subcutaneous tissues in proximity of the scar and within the surgical bed. Ultrasound scan with FNAC may help in discriminating RPA nodules from other lesions, such as amputation neuroma of the great auricular nerve or reactive lymph nodes. Since multiple nodules may occur and also extend to involve deep neck spaces (e.g., parapharyngeal, masticatory, neck soft tissues – level II), cross-sectional imaging is mandatory before treatment planning, and contrast-enhanced MR is considered the technique of choice. Key information is provided by T2 sequences: RPA, similar to primary lesions, shows a characteristic hypersignal that is more evident when the signal of fat tissue is artificially suppressed during the acquisition ( Fig. 41.1 ). After contrast medium administration, findings are more variable, ranging from a cystic appearance (peripheral or completely absent enhancement) to a solid pattern (vivid, though more commonly heterogeneous enhancement) ( Fig. 41.2 ). Diffusion-weighted imaging sequences may be of help, as they increase the contrast between the nodule and background tissues, both on the acquired set of images and in the retrospectively calculated apparent diffusion coefficient (ADC) map. Given the higher specificity of T2 findings, contrast administration may be avoided in selected cases, such as in the scenario of MR monitoring the growth rate of tiny lesions.
Surgical Treatment of Recurrent Pleomorphic Adenoma
Surgery, even if challenging, is considered the treatment of choice for RPA, leaving observation only for elderly subjects, patients with relevant comorbidities, or in the presence of small lesions until they start to grow. Treatment should be tailored according to the original surgical procedure and local extent of the relapse; regardless of the entity of first surgery, skin scar should be resected to remove possible neoplastic seedings ( Fig. 41.3 ).
