Differential diagnosis of fat-containing lesions in the inguinal canal using ultrasound
Article Category: research-article
Pubblicato online: 30 set 2019
Pagine: 222 - 227
Ricevuto: 01 gen 2019
Accettato: 19 lug 2019
DOI: https://doi.org/10.15557/jou.2019.0033
Parole chiave
© 2019 Andrzej Smereczyński et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
There are several sites of reduced strength in the abdominal wall. Symmetrical inguinal canals, which are the most common location of hernia, are one of such sites. Furthermore, other pathological lesions that should be included in the differential diagnosis may be found here. The aim of the paper is to present fat-containing lesions located in the inguinal canal based on both our own experience and literature.
The inguinal canal is formed in the third trimester of pregnancy or, in some cases, in the first year of life. The development of this tissue tunnel is accompanied by the descent of the gonads to the pelvis, particularly the testes, which penetrate through the anterior hypogastric wall to the scrotum, pulling behind the fascia, the transverse and internal oblique muscle fibers and the parietal peritoneum. In the earlier period (about 7 weeks gestation), a gubernaculum occurs, comprised mostly of connective tissue, whose role is to pave the way for and support testicular descent. The peritoneal vaginal process develops during this period, which initially takes the form of a peritoneal recess, to later close and fuse with the spermatic cord, and finally close the inguinal canal. When this process is impaired, retroperitoneal fat or, less commonly, peritoneal viscera or fluid may penetrate into the patent vaginal process, which will clinically manifest as a (potentially painful) tissue bulge at this site. The inguinal canal is mostly made of fascia, aponeurosis and muscle fibers. The deep inguinal ring is an entrance to the canal, whereas the superficial inguinal ring is the external opening of the canal. In males, the lumen of the inguinal canal, which is 3–4 cm long, is tightly filled with the spermatic cord along with its vessels and nerves (Fig. 1 A and B). The female canal, which is narrower and shorter, contains only the round ligament of the uterus, which extends to the large pudendal lip (Fig. 2). The female canal is referred to as the “canal of Nuck” in English literature. It should be noted that the inferior portion of the inguinal canal is adjacent to the inguinal ligament, which extends between the upper anterior iliac spine and the pubic tubercle(1–6). Furthermore, the inferior epigastric vessels, which are located posteriorly to the inguinal canal and medially of the internal inguinal ring, are an important diagnostic landmark(1–6). These structures help properly apply a linear transducer of at least 7 MHz. When scanning the canal in the long axis, the transducer should be placed parallel, just above the inguinal ligament, whereas transverse scanning should be used to visualize its width. The use of Doppler option to visualize the vasculature of the spermatic cord may help ensure correct imaging site (Fig. 3). Convex transducer (3–5 MHz) may prove helpful in obese patients. Functional tests, such as the cough test and the Valsalva maneuver, as well as transducer compression and scanning in a standing position, are important elements of the assessment(4,6).
Fig. 1.
Fig. 2.
Fig. 3.
In obese men, the spermatic cord shows uniform thickening, enhanced echogenicity and a large diameter (Fig. 4). During the Valsalva maneuver, a minor sliding may be observed, which should not be misinterpreted as a movable hernia(2).
Fig. 4.
In many publications, the term “spermatic cord lipoma” or “round ligament lipoma” is used to refer to retroperitoneal fat despite the fact that the authors using this term are aware of its inaccuracy(7–11). This form of fat is encountered intraoperatively in 2.3 to 72.3% of cases(7–11). As already mentioned, the peritoneal vaginal process may not close during embryogenesis, forming an open space along the long axis of the canal. This space is usually filled by different combinations of intestines, greater omentum or peritoneal fluid. Retroperitoneal fat enters the inguinal canal usually with overgrown vaginal process. Our non-published studies on inguinal hernia (
Fig. 5.
Fig. 6.
The greater omentum is a structure morphologically similar to preperitoneal fat. It is plastic, non-vascularized in color Doppler, with a mosaic echostructure and slightly higher echogenicity compared to the retroperitoneal fat. It connects with a mass of similar appearance located under the anterior abdominal wall rather than the fat in the lumbar region (Fig. 7). Ultrasonography enables the differentiation between the greater omentum and a pseudolipoma; however, we found no literature data to support this.
Fig. 7.
Lipoma is a benign encapsulated tumor, sometimes with distinct lobar structure, usually spindle-shaped and showing higher echogenicity compared to subcutaneous fat (Fig. 8). Lipomas with low stromal content may show lower echogenicity. The absence of connection with abdominal fat and the usual absence of vascularization in color Doppler are important features of this tumor. It is suggested that lipoma develops from the remnant gubernacular fat(6,12–15).
Fig. 8.
A hibernoma, i.e. lipoma originating from brown fat tissue, is a rare finding. It shows thermo-energetic properties. The tumor showed mixed echogenicity in a case report presented by San Miguel
Only 5% of all sarcomas, which are classified into 50 types, are located in the genitourinary tract. Liposarcoma (37%) and leiomyosarcoma (24%) are most commonly found in the inguinal canal. Malignant histiocytic fibroma comes third (10%), whereas fibrosarcomas come fourth (5%). Liposarcomas are usually large, rapidly growing, solid and usually heterogeneous. They display chaotic vascular pattern in Doppler ultrasound (Fig. 9 A and B). Although the tumor shows locally aggressive growth pattern, lymph node involvement and blood dissemination are uncommon. Radical orchiectomy and high resection of the spermatic cord, combined with radiation therapy in some cases, is an optimal management in this pathology(6,15,17–19). In doubtful cases, computed tomography (CT) or magnetic resonance imaging (MRI) should be performed, which allow for a more accurate assessment of the ongoing inguinal pathological processes(6,15). Ultrasound-guided biopsy may be needed in some cases.
Fig. 9.
Differential diagnosis of the above mentioned lesions should include many pathologies that can mimic them. First of all, the fat tissue surrounding the epigastric vessels should be mentioned. Its appearance is identical to that of retroperitoneal fat filling the hernial sac (Fig. 10). The exact topography of these vessels along with the fat cuff is shown in Fig. 11.
Fig. 10.
Fig. 11.
The true lipoma can be also mimicked by a lymph node affected by lipomatosis (Fig. 12); however it is located outside the inguinal canal. An undescended testicle present in the inguinal canal should be also mentioned. It usually manifests as a slightly hypoechoic lesion (Fig. 13). Therefore, the importance of a comprehensive ultrasonographic assessment in men, including the groin and the scrotum, should be emphasized. Similarly, an ovary may be found in the female inguinal canal. A precise assessment usually allows to identify the Graafian follicles (Fig. 14). Pelvic assessment to check for a potentially missing ovary is also important. An echogenic tumor may be sometimes mimicked by an intestine in the hernial sac (Fig. 15). In such cases, doubts can be resolved by repeated ultrasound after an intake of 500 mL of water by the patient. An incarcerated omentum will produce a similar ultrasound picture. The imaging conditions in this region are significantly compromised by postoperative scars, sutures and meshes. Differential diagnosis should include local primary and secondary proliferative lesions, which requires the diagnosis to be extended with CT or MRI.
Fig. 12.
Fig. 13.
Fig. 14.
Fig. 15.
Ultrasonography is a method of choice in the diagnosis of inguinal lesions provided that proper methodology and adequate anatomical knowledge are ensured. Differential diagnosis should include many clinically insignificant and significant lesions to ensure accurate diagnosis. In the case of doubts, CT or MRI and, in justified cases, ultrasound-guided biopsy, should be the next diagnostic step.