Keywords
schwannoma - intra-articular tumor - knee joint schwannoma
The infrapatellar Hoffa's fat pad (HFP) is an intracapsular but extrasynovial structure
located in the knee joint. Disorders of the HFP are a common cause of anterior knee
pain.[1] Published studies have reported that tumors, categorized as either diffuse or solitary,
can develop in the HFP. Solitary tumors are uncommon and mostly benign; among these
tumors, schwannomas are extremely rare.
Benign schwannoma is the most common tumor of the peripheral nerves. Schwannomas are
usually encapsulated, circumscribed, solitary, and located eccentrically and composed
of the Schwann cells of the peripheral nerve sheath. Malignant transformation of schwannomas
is extremely rare and accounts for less than 1% of all cases.[2] Schwannomas usually grow slowly and asymptomatically and are often detected incidentally.[3] In some cases, schwannomas may present symptoms, such as a lump, pain, or swelling.
Histologically, schwannomas have two distinctive areas of high and low cellularity
called Antoni A and B areas, respectively. Schwannomas are usually entirely composed
of Antoni A areas, where spindle cells are closely packed.
To the best of our knowledge, only one case of intra-articular schwannoma of the knee
has been reported. Thus, in the current report, we aim to describe a rare and interesting
case of an intra-articular schwannoma of the knee to increase its awareness in the
orthopaedic community.
Discussion
Most solitary HFP tumors are benign. In 2011, Dean et al presented 19 patients with
benign tumors of the intra-articular ganglia with pigmented villonodular synovitis
as the most common diagnosis.[4] In 2013, Albergo et al presented 25 patients who were most commonly diagnosed with
pigmented villonodular synovitis and hemangioma; two malignant tumors were reported,
and none of those were diagnosed with schwannoma.[5] Despite its rarity, schwannoma should be considered in the differential diagnosis.
The present case report describes the discovery of an intra-articular benign tumor
of the peripheral nerves. Schwannomas usually occur in the fourth and fifth decades
of life and have a female predilection of 1.6:1.[6] Schwannomas are often asymptomatic and discovered incidentally owing to their slow
growth. In the present case, the patient's pain corresponded with the progressive
tumor growth. In the literature, solitary tumors have been reported in various locations;
however, their occurrence in the lower limbs is rare.[7] To the best of our knowledge, only one case report has described an intra-articular
schwannoma of the knee.[8]
Evaluation of the patient's symptoms, history taking, and physical examination suggested
the presence of a tumor. Microscopic analysis helped to confirm the diagnosis of a
schwannoma. The patient's preoperative plain radiographs and MRI were assessed. Consequently,
radical surgical excision was proposed and performed based on the patient's symptomatology.
Although radiography should be initially performed to rule out the possibility of
malignant tumor, MRI remains the imaging technique of choice for accurate diagnosis.
Regarding solitary tumors, they are frequently symptomatic, and excellent outcomes
can be achieved using open excision, which ensures that solitary HFP tumors are completely
removed.[4]
Conclusion
This is the second reported case of a larger intra-articular schwannoma of the knee
since 1994. Considering the rarity of this tumor, the present report is a great addition
to the limited literature.
