Pathology of intra-articular tumours and tumour-like lesions: pearls, pitfalls and rarities from a general surgical pathology practice

Intra-articular tumours are uncommonly encountered in routine practice and may present diagnostic challenges to pathologists. Challenges unique to this site include distinction from more common reactive synovial conditions, which are far more common; histologic variability; superimposed reactive changes; and often, lack of provided clinicoradiological context. This article reviews the pathology of the synovial tumours and tumour-like lesions, including diagnostic pearls, pitfalls and rare entities.

Presence of a t(12;18)(q14;q21) Chromosome Translocation and Fusion of the Genes for High-mobility Group AT-Hook 2 (HMGA2) and WNT Inhibitory Factor 1 (WIF1) in Infrapatellar Fat Pad Cells from a Patient With Hoffa's Disease

BACKGROUND/AIM

Hoffa's disease is anterior knee pain presumably stemming from inflammatory fibrous hyperplasia of the infrapatellar fat pad (Hoffa's pad). The etiology and pathogenesis are unclear, however, and no genetic information about the disease has been published. We report the genetic findings in cells from the fat pad of a patient with Hoffa's disease.

MATERIALS AND METHODS

Infrapatellar fat pad cells from a patient with Hoffa's disease were examined using cytogenetic, RNA sequencing, reverse transcription-polymerase chain reaction, and Sanger sequencing techniques.

RESULTS

Cytogenetic examination of short-term cultured cells from the Hoffa's pad revealed a balanced t(12;18)(q14;q21) translocation as the sole chromosomal aberration. RNA sequencing detected an out-of-frame fusion of exon 3 of the gene coding for high mobility group AT-hook 2 (HMGA2) with exon 9 of the gene coding for WNT inhibitory factor 1 (WIF1). The fusion was subsequently verified by reverse transcription-polymerase chain reaction together with Sanger sequencing.

CONCLUSION

Our data indicate that Hoffa's disease is a neoplastic process with acquired genetic aberrations similar to those found in many benign tumors of connective tissues. The genetic aberrations are presumably acquired by mesenchymal stem cells of the infrapatellar fat pad inducing proliferation and differentiation into adipocytes or other mature connective tissue cells.

Para-articular Osteochondroma of Patella with Coexisting Osteoarthritis

INTRODUCTION

Para-articular osteochondromas are rare osteocartilaginous tumors arising adjacent to the joint, more common around the knee. In contrast to osteochondroma, they occur in elderly patients.

CASE REPORT

We report a 60-year-old female with slow-growing, extraosseous soft tissue mass in the infrapatellar fat pad region with coexisting osteoarthritis. Total excision of the mass with total knee arthroplasty (TKA) done. The patient had excellent functional outcome with no recurrence at 2-year follow-up.

CONCLUSION

The incidence of para-articular osteochondromas in elderly patients with coexisting osteoarthritis is very rare. Clinicoradiological features along with histopathology confirm its diagnosis. Total excision is the mainstay of treatment along with TKA if there is coexisting arthritis and its recurrence is very rare.