Distribution Patterns of Benign and Malignant Bone and Soft Tissue Tumors and Tumor-like lesions in the Hindfoot and Ankle: A 12.5-year Analysis

Discussion

Swellings and masses in the complex anatomical area of the ankle and hindfoot are common reasons for medical presentation and can easily be detected due to the relatively thin subcutaneous tissue (7). However, various pathologies can be their cause, such as trauma, infections, metabolic disorders, cardiovascular insufficiency, lymphedema, and tumorous entities. The incidence of the latter is higher than commonly thought. In a large series, 8% of benign and 5% of malignant soft tissue tumors occurred in the foot and ankle (12). Magnetic resonance imaging is essential for distinguishing these lesions, however, the distinction can be challenging in some cases (13, 14).

Understanding the incidence and anatomical distribution patterns of lesions is crucial for accurate assessment and appropriate management (15, 16). This study aimed to comprehensively analyze the bone and soft tissue lesions in the hindfoot and ankle over a 12.5-year period at a German University Hospital. We intentionally decided to include all lesions presented in our multidisciplinary tumor board, including pseudotumor and tumor-like lesions to support clinical practitioners in their daily work. This included diverse histopathological entities including ganglion cysts, epidermoid cysts, gouty tophi or rheumatoid nodules (17).

For the purpose of localization, we adopted the classification system used by Toepfer et al., who expanded the anatomical system proposed by Ruggieri et al. to categorize the foot into forefoot, midfoot, hindfoot, and the ankle (17). For our study, we focused on the hindfoot (talus and calcaneus) and ankle (epi-metaphysis of the distal tibia and fibula), separated by the ankle joint line.

Over the study period, our multidisciplinary tumor board discussed a total of 112 hindfoot and ankle pathologies. Of these, 105 lesions had a confirmed histopathologic diagnosis and were subjected to further evaluation. In general, soft tissue lesions were found to be significantly more frequent, accounting for 81.9% of cases evaluated. Additionally, 8.6% of cases presented to the multidisciplinary musculoskeletal tumor board were found to be malignant, highlighting the importance of accurate clinical and radiological assessment despite the predominance of benign, often harmless alterations (91.4%). In this study, only soft tissue lesions were affected by malignancy, which may be due to the small sample size of cases with osseous lesions. The malignancy rate is lower than that reported in former studies, possibly because we included pseudotumor and tumor-like lesions (6).

Overall, female patients were found to have a slightly higher incidence of 56.2% compared to males with 43.8%. Chou et al. reported an increased incidence of soft tissue and bony lesions of the foot and ankle in women with a rate of 54.9% (18). Interestingly, women were affected approximately twice as often by the three most common entities in our study, TGCT, schwannoma, and intraosseous ganglion. It is possible that differences in footwear, aesthetic demands or body consciousness of women may have contributed to these differences. On the other hand, gout tophi, epidermoid cysts, and chronic synovialitis were only found in male patients. The sex ratio for malignant tumors was relatively even.

The average age of patients diagnosed with malignant diseases was 59.2 years, which was significantly higher than the average age of patients with benign conditions at 40.8 years of age. However, it is important to note that both groups showed a wide range of ages, leading to considerable overlap. Therefore, relying solely on age or sex as a factor should not be sufficient for excluding or confirming a disease in individual cases.

Overall, more than two thirds of all cases occurred at the hindfoot (n=72) and benign soft tissue lesions at the hindfoot represented more than half of all cases (n=58). Benign soft tissue lesions of the ankle were found in 19 cases. Osseus lesions showed a balanced distribution between the ankle and hindfoot. Malignant soft tissue tumors were also evenly distributed between the two study areas, with four cases in the hindfoot and five cases in the ankle. As there were three times as many benign soft tissue lesions in the hindfoot as in the ankle, the malignancy rate in the hindfoot was significantly lower at 5.6% compared to 15.2% in the ankle. On the entity level, the three most common soft tissue entities showed a tendency to appear at the hindfoot rather than the ankle. However, 55.6% of the malignant entities, 47.4% of the osseous lesions, and almost a quarter of the benign soft tissue lesions appeared in the ankle, which underlines the necessity to consider this area (15).

The largest group, benign soft tissue lesions, comprised 18 different entities and accounted for 73.3% of all cases. TGCT had the highest incidence, followed by schwannoma, ganglion cyst, hemangioma, and lipoma. These top five entities accounted for 68.8% of all 77 benign soft tissue lesions.

TGCT, formerly known as pigmented villonodular synovitis (PVNS), was the most common benign soft tissue lesion, with 19 cases and 73.7% of its manifestations at the hindfoot. It is a rare lesion of the synovium that affects joints, tendon sheaths, and bursae and has been reported to be one of the most common soft-tissue tumors of the foot and ankle (15, 18, 19). The ankle is the second most frequently impacted joint, accounting for 14% of diffuse TGCT, after the knee joint with 64% (20). Nevertheless, TGCT can arise from any part of the foot and ankle region (21) and was observed in 13 female and 6 male patients in our study, with an average age of 27.7 years. Previous studies indicate that about 55% of all cases are female, and onset typically occurs in the third to fifth decade of life (21-23). Surgical excision remains the preferred treatment option (24-26). According to a systematic literature review by Siegel et al., the recurrence rate ranges from 7% to 21%, making radiological follow-up necessary (23).

The second most frequent diagnosis was schwannoma, which accounted for 17 cases. Schwannomas are slow-growing solid tumors that originate from Schwann cells in the peripheral nerves (27-29). They have been reported to be relatively rare in the foot and ankle region, with only 9.2%-11.5% of schwannomas being found there (18, 28, 30-32). Toepfer et al. observed 11 cases in 104 benign soft tissue tumors in the foot and ankle region (15). Another study by Ruggieri et al. identified six cases of schwannomas in sixteen benign tumors observed in the hindfoot, excluding pseudotumoral lesions (31). Our analysis revealed a preference of schwannomas for the hindfoot, with 15 out of 17 occurrences observed in this area. The average age was 50.8 years, ranging from 21 to 78 years. These findings are consistent with a review conducted by Hao et al., who reported an average age of 47.4 years and noted that over 80% of the tumors were located on the ankle, heel, and plantar aspect. However, like TGCT, schwannomas can occur in any part of the foot. In contrast to our observations that showed a higher incidence among women (11 cases) compared to men (6 cases), Hao et al.’s study found no sex disparities (27).

In our study, the ganglion cyst was found to be the third most common soft tissue lesion. It has been reported as the most prevalent tumor-like lesion in the foot and ankle region, accounting for approximately 42% of cases and affecting about 6% of the population (33, 34). The cysts are filled with mucopolysaccharides and typically appear near a joint capsule or tendon sheath. They may have communication with these structures and are believed to originate from mucoid degeneration (5, 17, 35, 36). Ultrasound and MRI imaging can effectively visualize and locate these cystic lesions (17, 37).

Hemangioma and lipoma accounted for four cases each, occurring in middle-aged patients without a significant sex preference. According to Kransdorf et al., hemangiomas were found in 8% of the total population (38,484 individuals), with 14% of cases found in the lower extremities (12). Studies on lower extremity hemangiomas have shown varying incidences within the foot, ranging from 4.9% to 28.5% (38, 39). It is widely accepted that these hemangiomas are caused by developmental abnormalities originating from endothelial cells (12, 39). Lipomas, on the other hand, typically arise on the dorsum of the foot (13).

Concerning osseus lesions, we found that intraosseous ganglion cysts were the most common lesion, accounting for 12 out of 19 cases. Previous studies have identified intraosseous ganglia as one of the most prevalent benign lesions (6). The exact cause and development process of these cysts are again not fully understood; however, it is widely believed that they may arise from acute or repetitive trauma, leading to degeneration in the surrounding connective tissue (40-42).

During our study period, a total of nine malignant soft tissue tumors were identified, spread across seven different entities. This shows the rarity, heterogeneity, but also the importance of keeping an eye on possible malignant differential diagnoses in tumors of the foot and ankle and illustrates the need for a histopathological examination (43). It should be emphasized that swelling may occur without the presence of a tumor, and conversely, a tumor may be present without severe swelling. This is especially true for bone tumors, where swelling usually occurs at a later stage (6, 9, 44).

Study limitations. It is important to recognize that the data utilized for this research were obtained from a singular healthcare facility, which may limit the generalizability of our findings. Furthermore, our facility specializes in the treatment of musculoskeletal tumors in patients who typically have more advanced or severe symptoms. This could introduce bias in sample selection and potentially affect the applicability of our results. Most of the cases analyzed underwent surgical intervention, which may have excluded benign and asymptomatic cases not addressed by our multidisciplinary musculoskeletal tumor board.