Hoffa's Fat Pad-associated Solitary Neurofibroma as the Cause of Anterior Knee Pain: A Case Report

Abstract

Introduction: Infrapatellar peripheral neural tumors, particularly neurofibromas, are rather rare entities reported in the literature. They are slow-growing lesions that usually do not exhibit clinical manifestations other than interspecific swelling or pain; hence, their diagnosis can be quite challenging. Therefore, scrutiny should include not only traditional clinical assessment and imaging but also more specific molecular biology techniques, such as immunohistochemistry.

Case report: We present the clinical, imaging, histological, and immunohistochemical features of a unique case of solitary neurofibromain a 33-year-old female presenting chronic anterior knee pain. The tumor was completely removed through a surgical approach.

Conclusions: Although cases of a solitary neurofibroma originating within Hoffa's fat pad are extremely rare; the entity should be considered in the differential diagnosis when symptomatology is not alleviated with appropriate treatments.

Keywords: Anterior knee pain; Hoffa’s fat pad; immunohistochemistry; solitary neurofibroma.

Figure 1

(a) Lateral, (b) anterior, and (c) transversal views of magnetic resonance imaging using gadolinium-based contrast medium.

Figure 2

H and E staining for transoperatory incisional biopsy.

Figure 3

Immunohistochemistry staining for (a) PS100, (b) CD34, (c) EMA, and (d) GFAP antibodies.

Figure 4

Surgical excision of the neoplasm: (a) Anterior knee approach and (b) Hoffa’s fat pad wide resection.

Figure 5

(a) Real-time -i.e., fresh- external surface of Hoffa’s fat pad and (b) fixed -10% paraformaldehyde buffer- and stained tissue for margin delimitation.

Figure 6

H and E staining for definite excisional diagnosis.

Figure 7

Postsurgical clinical evolution of the knee: (a) 1 day, (b) 1 week, (c and d) 2 weeks, (e) 3 weeks, and (f) 1 month after intervention.