Volume/Shape. The shape and size of a tumor can provide information of the type of tumor. Most BCC are anechoic and have a roughly elliptical shape; occasionally, they are elongated anechoic and have a collar necklace or rosary pattern (Fig. 13.3). SCC are also hypoechoic, but a thick superficial crust needs to be removed before visualization [4]. They are usually thick lesions with irregular “iceberg” shapes. HFUS imaging will be of great help in choosing the proper site for biopsy or selecting the best method for tumor removal. In addition, some tumors have an iceberg shape: they appear small at the surface while the length underneath the surface is larger. This could be the cause of positive margins after surgery.

Depth. The knowledge of the depth of tumors helps in deciding the correct surgical technique. For example, superficial BCC lesions can be diagnosed by clinical/dermoscopy [8] examination. Treatment options include cryosurgery, topical immunomodulators like imiquimod, photodynamic therapy (PDT), and curettage/electrocoagulation, among others. There is no need for costly, lengthy, expensive, and invasive techniques like Mohs micrographic surgery on a superficial carcinoma. Although this seems logical, the out-of-proportion use of Mohs surgery (1 out of every 4 tumors are treated with MMS [9]) suggests that this technique is being used for treating many superficial lesions. The HFUS image of a superficial BCC shows a hypoechoic elliptical area(s) of less than 1 mm of depth. Individually, each island of tumor measures 1–1.2 mm in depth. Lengthwise, they can be small (1–2 mm) but can also be quite large, requiring a segmental HFUS evaluation in order to cover the whole area. HFUS allows the determination as to whether BCC is only superficial or it has a deeper component within the tumor. Apparently “superficial BCC” can “hide” nodular or even morpheaform elements (admixture tumor), as is the case in roughly one-third of all BCC [10, 11] (Fig. 13.4a, b). The latter is a common cause of treatment failure and recurrence (Fig. 13.5). Sometimes this reoccurrence is many years later. The tumor’s depth has to be determined throughout the whole tumor area using HFUS readings. The deep margin evaluation by HFUS is limited to tumors under 8 mm in depth. Proper selection of the biopsy site is of utmost importance [12]; therefore, HFUS-guided biopsy could be another possible indication.

Length. The longitudinal/width margin evaluation by HFUS is limited to tumors under 12 mm. For large lesions, HFUS might need to be performed by sectors.