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Rhabdomyomatous mesenchymal hamartoma (RMH) is a subcutaneous lesion that is characterised by a normal epidermis overlying a dermis that contains randomly arranged mature striated muscle fibers associated with varying amounts of mesenchymal elements such as adipose tissue, collagen and blood vessels. Herein we report a mesenchymal hamartoma with rhabdomyomatous features occurring in the orbit.
A 2‐year‐old boy was referred to the clinic with a history of right unilateral axial proptosis presenting on the fourth day of life with no useful vision ipsilaterally. Two orbital biopsies had been performed, the first being unsuccessful, and the second showing haphazardly arranged skeletal muscle fibers and fibrous tissue. On examination, he had no light perception OD, ptosis, fixed extraocular movements, and a pale atrophic optic disc. Ultrasound features included a solid, well‐outlined highly reflective mass that was indenting the globe. Magnetic resonance imaging with gadolinium of the brain and orbit, at 5 months, revealed a diffuse infiltrative retrobulbar intraconal lesion. A repeat scan 18 months later, revealed an increase in the size of the lesion and the orbit (fig 11).). The initial differential diagnoses included mesenchymal hamartoma, benign soft‐tissue neoplasm, and granular cell tumour.
Due to the loss of vision, relentless increase in the size of the lesion, orbit, and superior orbital fissure, the patient underwent an eyelid and conjunctival sparing exenteration with lateral orbitotomy and a dermis fat graft.1 During surgery, the tumour felt firm and solid. The case was complicated by cerebrospinal fluid (CSF) leak one day postoperatively originating from the superior orbital fissure even though temporalis muscle with Tisseal® was used to patch the fissure intraoperatively. A lumbar drain inserted for 1 day resolved the CSF leak with no further complications. Histologic features are displayed in fig 22.
Two months later, the patient was fitted with an ocular prosthesis with good cosmetic outcome. He will undergo ptosis surgery in the future.
RMH was first described as striated muscle hamartoma in 1986 by Hendrick et al2 Since then, 30 cases of RMH have been recognized and reported in the literature.3,4,5,6,7,8 It is commonly seen in infants or young children and appears at birth. Clinically it presents as a firm, flesh‐coloured, nontender, polypoid, solitary subcutaneous lesion, at or near the midline, without prominent change in size. Specific congenital anomaly syndromes associated with RMH include Goldenhar and Delleman syndromes.3
In our case the histology was similar to that described for RMH; however it occurred in the orbit rather than the usual dermal and subcutaneous region. To our knowledge, this is the first such tumour reported in a non‐subcutaneous site.
The possibility of a benign Triton tumor was also considered but in these lesions the nerve and muscle tissue is intimately admixed as the muscle fibers are thought to have been entrapped within the nerve sheaths during development. As the main component of this tumour was skeletal muscle, with lesser contributions by peripheral nerve and adipose tissue, we are presenting this case as a unique occurrence of an orbital mesenchymal hamartoma with rhabdomyomatous features.
Informed consent has been obtained from the patient for the publication of their details.
Competing interests: none.