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Kaposi sarcoma of the glans: New findings by line field confocal optical coherence tomography examination

Dear Editor, Kaposi sarcoma (KS) is a low-grade vascular tumour associated with human herpesvirus 8 infection that commonly presents with multiple mucocutaneous lesions commonly classified in four main subcategories: classic, endemic, iatrogenic and epidemic.1 These forms are histologically indistinguishable but differ in epidemiology and prognosis. First presentation on the penis is rare (2%-3% of the KS cases), and it is more often observed in HIV patients.2 An otherwise healthy 67-year-old man presented with an asymptomatic micronodule on the glans noticed 4 months previously. Clinical history was negative for homosexual intercourses. Dermoscopic examination with polarized light showed a homogenous erythematous-violaceous background with irregular dilated linear vessels at the periphery (Figure 1A) and dotted vessels around the nodule, suggestive of a vascular lesion. Line field confocal optical coherence tomography (LC-OCT) 3D (DAMAE Medical®) examination was performed on the lesional (Figure 1A) and the peri-lesional skin (Figure 1B) up to a depth of 500 μm, each imaging having a lateral field of view of 1200 μm.3 To ensure the best visualization of the vascular structures, multiple examinations were carried out both by applying minimal pressure on the lesion surface (Figure 1A) and without pressure (Figures 1B and 2). Vertical in vivo LC-OCT images on central lesional area (Figure 1A) confirmed the presence of abundant vessels visible as elongated horizontal dark areas separated by solid structures. Short dark areas were visible in the papillary dermis corresponding to slit-like vessels (SLV) along with numerous large and long dark areas corresponding to vascular lacunae (VL) in the deeper dermis. Mucosal epithelium was normal and the dermo-epidermal junction (DEJ) was flattened and thin when pressure was applied on the probe. Vertical in vivo LC-OCT images performed without pressure (Figure 1B) showed thickened epithelium and non-flattened DEJ. Moreover, non-reflective small roundish areas corresponding to dilated capillary loops in the dermal papillae were visible at the periphery of the nodule. These vessels observed in 3D reconstruction corresponded to the dotted vessels visualized under dermoscopy. Elaboration of multiple no pressure acquisitions was performed with MinIP (3DSlicer version 4.10.2) to obtain 3D imaging and orthogonal views close to “virtual scan”: aberrant horizontally disposed SLV and VL were visible at ~100-200 μm depth in the centre of the lesion; sparse hyper-reflective spots probably corresponding to blood cell extravasation were also visible at this depth (Figure 2A). Detailed analysis of a peri-lesional area of 500 × 500 μm (Figure 2B) revealed hypo-reflective grape-like spaces in the papillary dermis corresponding to loop of vertically tortuous and dilated vessels rising in dermal papillae and reaching the DEJ. Multiple a-reflective structure corresponding to slit-like vessels and vascular lacunae were visible at ~100 μm and at ~200 μm depth, respectively. A punch biopsy was performed for histological examination that diagnosed KS (Figure 3). Routine laboratory investigation and lymphocytes subpopulation were normal, while HIV test was negative. Chest X-ray and abdominal ultrasonography did not show any visceral lesions. Few cases of KS with primary presentation on the penis in HIV negative men have been reported in the literature.2 The rainbow pattern, that is currently considered the most specific dermoscopic pattern of KS, was absent in our case. Lichen planus and genital hemangiomas could be considered as differential diagnoses. A single papule of lichen planus can share a similar clinical aspect and can be asymptomatic. However, dermoscopy usually highlights an homogenous pinkish background with of dotted/comma radially disposed vessels along with Wickham striae.4 Reactive hemangioma is particularly rare on the glands mucosa, especially in adults5 and it is characterized by clear-cut VL with jelly collarette on dermoscopy.6 LC-OCT is a new imaging technique that allows an in vivo acquisition of vertical and horizontal images very close to histology and reflectance confocal microscopy, respectively. In the present case, LC-OCT allowed us to detect an aberrant vascular proliferation and to identify solid tissue among vascular channel, differently from haemangioma that shows huge VL. Correlation between with histological slides enabled us to define the LC-OCT appearance of both SLV and VL in the centre of the tumour and of dilated capillary loops on the lesion margin, and to establish their link with the dermoscopy features. In addition, the LC-OCT visualization with minimal to no pressure applied allowed us to obtain a new imaging mode not affected by artefacts due to tissue stretching and/or alteration occurring during histological slide preparation. In particular, the 3D LC-OCT imaging detected vascular grape-like structures in dermal papillae reaching the dermal-epidermal-junction otherwise not visible in standard histologic preparations. Further examinations are needed to confirm the present findings and characterize them as specific for KS lesions. Although histological examination remains the gold standard in suspicion of KS,