Nerve injury associated with high-intensity focused ultrasound: A case report

Histological Changes of Porcine Animal Skin with Micro-focused Ultrasound

BACKGROUND

As a noninvasive alternative therapy, microfocused ultrasound (MFU) has become a research hotspot in recent years for its potential to enhance skin laxity. While several clinical studies have explored the effects of MFU on improving skin laxity, there is limited literature available on the histological changes resulting from MFU treatments. It has been established that the skin structure and composition of the Bama miniature pigs closely resembles that of humans, including collagen content, type I collagen distribution, and elastin distribution.

METHODS

This study primarily focuses on examining the histological alterations in the skin tissue of Bama miniature pigs following MFU application. We also selected some typical clinical photographs of patients treated with MFU and compared the clinical effects with histological changes observed in porcine skin. The MFU device utilized in this study incorporates ultra-pulse technology and large focal area technology.

RESULTS

Following the standard operating procedures provided by the manufacturer, different handles were used in different skin area of pigs. Biopsies were obtained immediately after treatment and 1 month after treatment. Significant histological changes were observed in the Bama miniature pigs skin, including collagen contraction and fragmentation, dilation and congestion of superficial dermal capillaries immediately after MFU treatment; dermal thickening, increased thickness and density of collagen fibers, elevated levels of elastin and type I collagen, as well as thickened fiber septa in the adipose layer 1 month later. These histological results corresponded to clinical findings in human, such as facial redness and swelling immediately after treatment, and improvement in facial relaxation after approximately 1 month after treatment.

CONCLUSION

Collectively, these histological findings provide valuable evidence supporting the clinical application of MFU for enhancing skin laxity.

NO LEVEL ASSIGNED

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In Vivo Non-Thermal, Selective Cancer Treatment With High-Frequency Medium-Intensity Focused Ultrasound

Focused ultrasound (FUS) has proven its efficacy in non-invasive, radiation-free cancer treatment. However, the commonly used low-frequency high-intensity focused ultrasound (HIFU) destroys both cancerous and healthy tissues non-specifically through extreme heat and inertial cavitation with low spatial resolution. To address this issue, we evaluate the therapeutic effects of pulsed (60 Hz pulse repetition frequency, 1.45 ms pulse width) high-frequency (20.7 MHz) medium-intensity (spatial-peak pulse-average intensity I_SPPA < 279.1 W/cm², spatial-peak temporal-average intensity I_SPTA < 24.3 W/cm²) focused ultrasound (pHFMIFU) for selective cancer treatment without thermal damage and with low risk of inertial cavitation (mechanical index < 0.66), in an in vivo subcutaneous B16F10 melanoma tumor growth model in mice. The pHFMIFU with 104 μm focal diameter is generated by a microfabricated self-focusing acoustic transducer (SFAT) with a Fresnel acoustic lens. A three-axis positioning system has been developed for automatic scanning of the transducer to cover a larger treatment volume, while a water-cooling system is custom-built for dissipating non-acoustic heat from the transducer surface. Initial testing revealed that pHFMIFU treatment can be applied to a living animal while maintaining skin temperature under 35.6 °C without damaging normal skin and tissue. After eleven days of treatment with pHFMIFU, the treated tumors were significantly smaller with large areas of necrosis and apoptosis in the treatment field compared to untreated controls. Potential mechanisms of this selective, non-thermal killing effect, as well as possible causes of and solutions to the variation in treatment results, have been analyzed and proposed. The pHFMIFU could potentially be used as a new therapeutic modality for safer cancer treatment especially in critical body regions, due to its cancer-specific effects and high spatial resolution.

Assessment of Enhanced Thermal Effect Due to Gold Nanoparticles during MR-Guided High-Intensity Focused Ultrasound (HIFU) Procedures Using a Mouse-Tumor Model

An in vivo study was conducted using a mouse tumor model, to assess the utility of using gold nanoparticles (gNPs) during HIFU procedures to locally enhance heating at low powers. Tumors were grown using melanoma tumor cells (B16/F10) subcutaneously on the right flanks of mice (C57Bl/6J). Physiologically relevant concentrations (0 and 0.125%) of gNPs were directly injected into the tumors. Sonications at acoustic powers of 10 and 30 W were performed for a duration of 16 s inside a magnetic-resonance system. Temperature increases and lesion volumes were calculated and compared for procedures with and without gNPs. Histopathology study was conducted using a cleaved caspase 3 antibody and hematoxylin and eosin staining after removing the tumors from the mice. For an acoustic power of 30 W, end-of-sonication temperature increases of 25.4 ± 3.8 °C (0% gNP) and 42.2 ± 4.6 °C (0.125% gNP) were measured. Using cleaved caspase 3 antibody, it was observed that more than 1% of nuclei are affected in the case of 0.125% and 30 W but only 0.01% of nuclei are affected in the 0% case. For 30 W and a gNP concentration of 0.125%, a lesion volume of 0.33 ± 0.22 mm³ was obtained, while no lesion was observed without gNP's.

Facial Nerve Injury and Repair: A Practical Review for Cutaneous Surgery

BACKGROUND

The facial nerve and its branches are at risk of injury during dermatologic surgery. Few publications in the dermatologic literature discuss facial nerve injury and management.

OBJECTIVE

To review facial nerve injury and management, including static and dynamic repair techniques, and to review outcomes in facial nerve reconstruction.

METHODS

Two detailed literature reviews were performed using PubMed. First, articles reporting facial nerve injury and/or management in the dermatologic literature were identified. In addition, articles pertaining to outcomes in facial nerve reconstruction with a minimum of 20 patients were included.

RESULTS

Fifty-three articles reporting outcomes in facial nerve reconstruction were identified and consist of retrospective reviews and case series. Most patients achieve improvement in facial symmetry and movement with nerve repair.

CONCLUSION

Timing of facial nerve repair is an important consideration in management of facial nerve injury, with earlier repairs achieving better outcomes. Facial nerve repair does not result in normal facial movement, and improvements may require a year or more to be realized. Many options exist for facial nerve reconstruction, and patients with long-standing facial nerve injuries may still benefit from treatment.